all: don't use gchar/gshort/gint/glong but C types

We commonly don't use the glib typedefs for char/short/int/long,
but their C types directly.

    $ git grep '\<g\(char\|short\|int\|long\|float\|double\)\>' | wc -l
    587
    $ git grep '\<\(char\|short\|int\|long\|float\|double\)\>' | wc -l
    21114

One could argue that using the glib typedefs is preferable in
public API (of our glib based libnm library) or where it clearly
is related to glib, like during

  g_object_set (obj, PROPERTY, (gint) value, NULL);

However, that argument does not seem strong, because in practice we don't
follow that argument today, and seldomly use the glib typedefs.
Also, the style guide for this would be hard to formalize, because
"using them where clearly related to a glib" is a very loose suggestion.

Also note that glib typedefs will always just be typedefs of the
underlying C types. There is no danger of glib changing the meaning
of these typedefs (because that would be a major API break of glib).

A simple style guide is instead: don't use these typedefs.

No manual actions, I only ran the bash script:

  FILES=($(git ls-files '*.[hc]'))
  sed -i \
      -e 's/\<g\(char\|short\|int\|long\|float\|double\)\>\( [^ ]\)/\1\2/g' \
      -e 's/\<g\(char\|short\|int\|long\|float\|double\)\>  /\1   /g' \
      -e 's/\<g\(char\|short\|int\|long\|float\|double\)\>/\1/g' \
      "${FILES[@]}"

src/main-utils.c

@@ -177,7 +177,7 @@ nm_main_utils_ensure_not_running_pidfile (const char *pidfile)
 	gs_free char *contents = NULL;
 	gs_free char *proc_cmdline = NULL;
 	gsize len = 0;
-	glong pid;
+	long pid;
 	const char *process_name;
 	const char *prgname = g_get_prgname ();