glsl: Be consistent about '\n', '.', and capitalization in errors/warnings.

The majority of calls to _mesa_glsl_error(), _mesa_glsl_warning(), and
_mesa_glsl_parse_state::check_version() use a message that begins with
a lower case letter and ends without a period.  This patch makes all
messages follow that convention.

Also, error/warning messages shouldn't end in '\n', since
_mesa_glsl_msg() automatically adds '\n' at the end of the message.

Reviewed-by: Matt Turner <mattst88@gmail.com>

src/glsl/ast_function.cpp

@@ -626,7 +626,7 @@ process_vec_mat_constructor(exec_list *instructions,
     *      int i = { 1 }; // illegal, i is not an aggregate"
     */
    if (constructor_type->vector_elements <= 1) {
-      _mesa_glsl_error(loc, state, "Aggregates can only initialize vectors, "
+      _mesa_glsl_error(loc, state, "aggregates can only initialize vectors, "
                        "matrices, arrays, and structs");
       return ir_rvalue::error_value(ctx);
    }