What does the file extension ".hg" mean?

[John Emmas <johne53 tiscali co uk>]

or to ask a better question...  "how up to date are the MSVC project 
files that come with glibmm?"

I just tried to build glibmm using MSVC 2005.  The supplied MSVC project 
contains these four "cc" files as the first 4 source files in its list:-

        balancedtree.cc
        bytearray.cc
        bytes.cc
        checksum.cc

However, if I try to compile any of those files (or indeed, most of the 
others) I get an error saying that the relevant file doesn't exist 
(which it doesn't).  Taking those four files as an example, although I 
can't find any such files with the extension ".cc", I do find equivalent 
files having the extension ".hg".  It looks like each ".hg" file should 
somehow get converted to its equivalent ".cc" file.  Should that 
conversion be getting done by the MSVC solution - or do I need to run 
some kind of pre-build step?

'README.win32' suggests that I should simply be able to load the MSVC 
solution and then build it, without first needing to do anything special 
- except for adding the relevant 'include' and 'lib' folders for my 
system.  Has something changed since the MSVC projects were 
constructed?  Or (like the README file suggests) should it be very 
simple to build immediately from the MSVC solution?

John