[RndTbl] .pc files and pkgconfig

[millward]

/usr/lib/pkgconfig/  .pc files
I've never heard of these things before and I
can't find any docs how to edit them correctly.
I was trying to install a program called  selectwn-0.4
which is suppose to allow you to change window
managers easily, but it won't install since it can't
'see' GLIB >= 2.0.0  Selectwn-0.4 says to 'edit'
my pkgconfig files, specifically  glib.pc.
I installed the required GTK library, glib-2.0.6.tar.gz,
and mucked about with glib.pc but it didn't work..
Has anyone out there ever edited one of these?
Is it even a good idea to mess with them?
I thought app programs where suppose to 'find' stuff
by looking in the PATH in .bash_profile.
Here is my original  glib.pc for GLib-1.2
  
prefix=/usr
exec_prefix=/usr
libdir=/usr/lib
includedir=/usr/include

Name: GLib
Description: C Utility Library
Version: 1.2.10
Libs: -L${libdir} -lglib
Cflags: -I${includedir}/glib-1.2 -I${libdir}/glib/include

The upgrade version to glib is in /usr/local/glib-2.0.6
I created a directory  /usr/include/glib-2.0.6 put
gmodule.h and gmodule.h version 2.0.6 in it.
/usr/local/glib-2.0.6 has at least 6 .pc files, none of
which have been transferred to /usr/lib/pkgconfig/
Should I put them there (Y/N)?
   I thought all this kind of stuff was suppose to be
done automatically when installing libraries in the
Linux these days. 
Somehow, I think I've made things worse.
Anybody got any good advice?