Update to 2.6.3.

• Add a generic check for deprecated macros (e.g. the recent autotools batch), and add USE_MESA to the set [1]
• Only use USE_LIBTOOL_VER for checking .la file installation [1]
• Add a check for USE_LIBLTDL and warn about directly using a libltdl dependency [1]
• Check distinfo to make sure each file in DISTFILES has SIZE and MD5 entries if NO_SIZE and NO_CHECKSUM are not defined

Submitted by: krion and tobez [1]