fix unicode handling in is_regular_file check - refs #2273
use FT_Open_Face instead of FT_New_Face - refs #1897

Conflicts:
	src/font_engine_freetype.cpp
fix boost directory iterator to use wide paths - closes #2273

Conflicts:
	src/font_engine_freetype.cpp
windows fix: declar miniz PNGWriter
windows build fixes in palette and miniz_png headers