[PATCH] small INSTALL file corrections

Hi,

following the INSTALL documentation I took the chance to correct a few
minor things I spotted.
Here's a patch containing the changes, in case you want to apply it to
the source (patch against trunk):

[[[
Several small updates/corrections to the INSTALL file:
- mention VS 2010 compatibility
- case-correction for February
- replaced dead-link to Platform SDK for VC6 with link to still
available instructions
- replaced redirection URL zlib.org with direct URL zlib.net
- update VS build instructions to be suitable for VS >= 2010
- added missing compatibility note for VS 2008

* INSTALL
     documentation updated
]]]

Regards,
Stefan