updated mingw build instructions for libssh2.

   If you have any problems linking libraries or finding header files, be sure

   to verify that the provided "Makefile.m32" files use the proper paths, and

   adjust as necessary.

   adjust as necessary. It is also possible to override these paths with 

   environment variables, for example:

     set ZLIB_PATH=c:\zlib-1.2.3

     set OPENSSL_PATH=c:\openssl-0.9.8d

     set LIBSSH2_PATH=c:\libssh2-0.15

   ATTENTION: if you want to build with libssh2 support you have to use latest

   sources fetched from CVS - the current 0.14 release will NOT work!

   Use 'make mingw32-ssh2-ssl' to build curl with SSH2 and SSL enabled.

   Cygwin

   ------

   documentation on how to compile zlib. Define the ZLIB_PATH environment

   variable to the location of zlib.h and zlib.lib, for example:

     set ZLIB_PATH=c:\zlib-1.2.1

     set ZLIB_PATH=c:\zlib-1.2.3

   Then run 'nmake vc-zlib' in curl's root directory.

   Before running nmake define the OPENSSL_PATH environment variable with

   the root/base directory of OpenSSL, for example:

     set OPENSSL_PATH=c:\openssl-0.9.7d

     set OPENSSL_PATH=c:\openssl-0.9.8d

   Then run 'nmake vc-ssl' or 'nmake vc-ssl-dll' in curl's root

   directory.  'nmake vc-ssl' will create a libcurl static and dynamic

MingW     http://www.mingw.org

OpenLDAP  http://www.openldap.org

Zlib      http://www.gzip.org/zlib/

libssh2   http://www.libssh2.org