update to version 1.2.7

Changes in 1.2.6.1 (12 Feb 2012)
- Avoid the use of the Objective-C reserved name "id"
- Include io.h in gzguts.h for Microsoft compilers
- Fix problem with ./configure --prefix and gzgetc macro
- Include gz_header definition when compiling zlib solo
- Put gzflags() functionality back in zutil.c
- Avoid library header include in crc32.c for Z_SOLO
- Use name in GCC_CLASSIC as C compiler for coverage testing, if set
- Minor cleanup in contrib/minizip/zip.c [Vollant]
- Update make_vms.com [Zinser]
- Remove unnecessary gzgetc_ function
- Use optimized byte swap operations for Microsoft and GNU [Snyder]
- Fix minor typo in zlib.h comments [Rzesniowiecki]