Modestmaps

- reinstated display of children for missing tiles, except when if
map.enablePyramidLoading is set to true

- added map.enablePyramidLoading flag for pyramid loading (off by default)
- fixed Coordinate.prototype.toKey (back to string join to avoid collisions)

- changed the order of initialization so that event handlers go last
(this is so that attributes like layerParent are in place for complex
event handlers like anyzoom.js... handlers can also use callbacks now)

2011-01-03 note:
- broke modestmap.js file into src folder, now building with Makefile
- no functionality change to modestmaps.js (just whitespace changes)

- changed to img.style.width instead of img.width, for ipads (see examples/touch/test.html)

- stubbed out tilePadding into Map.draw

- removing magic numbers from Mercator projection for parity with Python version