Apply knnniggett's solution on gnutls-openssl issue which

adds support for RPM based distros.

CMakeLists.txt

@@ -225,6 +225,10 @@ endif(GCRYPT_LIBRARIES)
 
 # gnutls (using find_library and find_path)
 find_library(GNUTLS_LIBRARIES gnutls-openssl)
+if(NOT GNUTLS_LIBRARIES)
+    find_library(GNUTLS_LIBRARIES gnutls)
+endif(NOT GNUTLS_LIBRARIES)
+
 if(GNUTLS_LIBRARIES)
 	set(HAVE_LIBGNUTLS 1)
 	list(APPEND ZM_BIN_LIBS "${GNUTLS_LIBRARIES}")