Show the right GnuTLS version when using ./configure --with-gnutls-dev
Show the right GnuTLS version when using ./configure --with-gnutls-dev

Previously the version information was always loaded from the
system-wide installation, now the pkg-config file from the GnuTLS git
tree is used if enabled.

airtower-luna/mod_gnutls,airtower-luna/mod_gnutls,airtower-luna/mod_gnutls