new API FT_Get_Gasp to return entries of the GASP table
corresponding to a given character pixel size.
* src/sfnt/ttload.c: add version check for the GASP table,
in order to be better future-proof
* include/freetype/config/ftheader.h: add definition of
FT_GASP_H, corresponding to <freetype/ftgasp.h>
* src/base/rules.mk, src/base/Jamfile, modules.cfg,
builds/win32/visualc/freetype.dsp,
builds/win32/visualc/freetype.vcproj: Adding src/base/ftgasp.c
to the default build