- remove some comments from configure.ac
- replace hand-written check for sa_family_t type with AC_CHECK_TYPES
- replace AC_CHECK_STRUCT_FOR with AC_CHECK_MEMBER
- fix spelling error in checking for mmap support
- partially rewrite checking for mmap, gunzip
- fix a code comment and use #ifdef HAVE_MMAP rather than #ifdef ENABLE_MMAP
- rewrite mmap/gunzip checking in configure
- remove explicit dmalloc and efence support