GnuTls: Fixed compilation of gnutlsxx

[address@hidden]

Hello,
I tried to compile GnuTls in Mingw+Msys and I got an error because 
gnutls/gnutls.h was not found with gnutlsxx.c
After a quick check I discovered that there was a mistake into lib/Makefile.am 
because there was a wrong hardcoded path to includes into 
libgnutlsxx_la_CPPFLAGS.
I guess the compilation had been possible with some luck if there was already 
a gnutls/gnutls.h installed into the global path. Otherwise, into an empty 
enviroment like mine, the compilation always aborted.
Attached patch fixes the problem.
I hope you will find this very little fix useful and it could be possible to 
commit it without the need of subscribing to bugzilla.

Greetings from Italy.

Sincerely,

Carlo Bramini.

gnutls.txt
Description: Text document