Removed bash-ism from bootstrap.sh.  (Not /bin/sh are bash, even these days.)
Bug fix: tests didn't (always) return a valid status.

gdImageAALine_thickness.c didn't explicitly return 0 on success.

gdimageline_bug5.c was not an actual test at all.  It now confirms that the
tested operation (a line draw) alters the image it draws on.  (Not ideal
but better than what it did before.)
Starting on simple MSYS makefile.
MSYS makefile builds basic DLL.
Builds w/ jpeg.
Added a rule to make the dep list.
Moved the deps to a different file.
Resulting DLL succesfully links to a test and runs.
Added script to run tests.
run_tests.sh now works.
Added support for TIFF and XPM (commented-out).
Added Windows products to .gitignore.
Added *.dll to .gitignore.
Added dummy deps.mk so make won't recreate it in wndows/msys/.
Prevented spurious generation of deps.mk.
run_tests.sh now takes extra C flags as an argument;
Makefile passes include paths to it, so the jpeg test can find its include file.
Added a README for the MSYS Makefile.
Merge branch 'private-msys-makefile' of github.com:imazen-discovery/gd-libgd into private-msys-makefile