the making of the release archive.
Added 'maketgz' as a script to build release archives with, including automated
snapshots or whatever. It updates the defines in include/libssh2.h.
configure now extracts the version number from the include/libssh2.h header in
the source tree instead of using it fixed set in the script (to remove the
need for regenerating the configure script when we run maketgz).
Makefile.am now has a dist-hook that puts ".dist" files in the release tree
instead of the file without the .dist extension, so that we can easily add
modified files in release archives. Like maketgz.
