Pkgconf

----------------------------

* Bug fixes:
- back out disabling the dependency resolver for single-package queries, it caused
too many regressions.

* Enhancements:
- allow explicitly disabling the dependency resolver via new environment variable,
PKG_CONFIG_MINIMUM_TRAVERSE_DEPTH=1. while pkgconf could already do this using
--minimum-traverse-depth=1, other pkg-config implementations do not have this
option, so adding an environment variable allows to make better use of this
feature (other implementations won't error due to unknown option this way)

----------------------------

* Bug fixes:
- rewrite handling of --modversion, --print-variables and --variable to not require
the dependency resolver
- ensure we disable the dependency resolver in all cases where it is a single-package
query (1.3.1 did not go far enough)

----------------------------

* Features:
- implement --short-errors

* Bug fixes:
- only consider a single package at a time with --print-requires, --print-requires-private,
--print-provides, --modversion, --print-variable and --print-variables

* Enhancements:
- synchronized latest freedesktop.org changes to pkg.m4
- improve error reporting with legacy --atleast-version and similar flags.

----------------------------

* Features:
- pkgconf --debug now provides a facility for tracing most relevant libpkgconf operations
- libpkgconf: add warn and trace handlers for warnings
- replace realpath() with faster, lighter weight path normalization function (github 112)
- pkgconf CLI now emulates pkg-config quoting rules precisely, while allowing direct access
to the actual fragments via libpkgconf

* Bug fixes:
- pkg: properly separate static and virtual packages so they are not inappropriately
optimized out of the dependency graph (github 108)
- argvsplit: do not consider ' and " to have similar rules to escape sequences (github 111)
- pkg: strip trailing whitespace when parsing .pc files

* Enhancements:
- argvsplit basically rewritten from scratch
- many code fixes spotted by coverity
- add PKG_CONFIG_DONT_RELOCATE_PATHS and --dont-relocate-paths environment variables to
disable path relocation feature if needed
- remove extra whitespace that was present for compatibility with older pkg-config releases
(github 113)

----------------------------

* Features:
- new --path option lists the .pc files which provided the requested dependencies
- new path relocation API: pkgconf_path_relocate(), which wraps functions such as
realpath() and cygwin_conv_path().
- new --with-path option adds a path to the search list
- new --define-prefix and --dont-define-prefix features enable automatic prefix
detection for relocatable SDKs. this is mostly useful on windows.

* Bug fixes:
- fragments: fix even more edge cases involving token concatenation
- path lists: don't attempt to collect path inodes if the filter is disabled
- path lists: explicitly avoid uninitialised data for the path inode cache
- client: properly handle --keep-system-cflags and --keep-system-libs

* Enhancements:
- windows: build libpkgconf as a DLL
- fragments: only munge fragments if sysroot_dir is actually set
- overall API: resolver flags have been moved to being a client-object setting
instead of used for every function invocation

----------------------------

* Features:
- new Provides system allows alternate .pc files to provide a dependency
- stable library API (with documentation): http://pkgconf.readthedocs.io/

* Enhancements:
- make it possible to programmatically declare dependencies instead of just using the parser
- testsuite migrated to run under kyua
- provide a libpkgconf.pc file for consumers to use
- pkgconf client: new --pure flag to enable dependency graph optimization in --static mode
- significant .pc parser speedups using bsearch(3).
- handle -idirafter in the same way as -isystem CFLAGS
- learn toolchain "system" paths from GCC environment variables, if present
- filter duplicate PKG_CONFIG_PATH (and other) entries by inode

* Bug fixes:
- fragments: fix another edge case involving empty tokens being concatenated onto previous tokens
(github 99)
- libpkgconf: remove dependencies on config.h in public headers