Verifying versions with "pkg-config --modversion" :
A wrong question will provide a reply different from the expected.
'pkg-config --modversion glib' : 'glib' = old style = 1.2
'pkg-config --modversion glib-2.0 : new style = 2.x.xx
I.e pkg-config looks for an exact match of names found in
/usr/lib/pkgconfig . No wild cards are allowed.
( Both the old "1.2" and the new 2.x version of glib / gtk are
supposed to be present in /usr/lib/ .(See install disk 1 //l/ ))
Installing to /usr/local/ is not an update, the system versions
are still present in /usr/ .
And it is not advisable to change glib2 / gtk2 to new versions.