added some comments for MingW32 builds.

   MingW32

   -------

   MinGW32 does not provide a batch script to set environment variables

   automatically. Make sure that MinGW32's bin dir is in PATH and then

   run 'mingw32-make mingw32' in the root dir. There are other make

   targets available to build libcurl with more features, use:

   Make sure that MinGW32's bin dir is in the search path, for example:

     set PATH=c:\mingw32\bin;%PATH%

   then run 'mingw32-make mingw32' in the root dir. There are other

   make targets available to build libcurl with more features, use:

   'mingw32-make mingw32-zlib' to build with Zlib support;

   'mingw32-make mingw32-ssl-zlib' to build with SSL and Zlib enabled;

   'mingw32-make mingw32-ssh2-ssl-zlib' to build with SSH2, SSL, Zlib;

   'mingw32-make mingw32-ssh2-ssl-sspi-zlib' to build with SSH2, SSL, Zlib

   and SSPI.

   and SSPI support.

   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

     set ZLIB_PATH=c:\zlib-1.2.3

     set OPENSSL_PATH=c:\openssl-0.9.8e

     set LIBSSH2_PATH=c:\libssh2-0.16

     set LIBSSH2_PATH=c:\libssh2-0.17

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

   sources fetched from CVS - the current 0.15 release will NOT work!

   version 0.17 - previous versions will NOT work with 7.17.0 and later!

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

   It is now also possible to build with other LDAP SDKs than MS LDAP;

   currently it is possible to build with native Win32 OpenLDAP, or with the

   Novell CLDAP SDK. If you want to use these you need to set these vars:

     set LDAP_SDK=c:\openldap

     set USE_LDAP_OPENLDAP=1

   or for using the Novell SDK:

     set USE_LDAP_NOVELL=1

   If you want to enable LDAPS support then set LDAPS=1.

   - optional MingW32-built OpenlDAP SDK available from:

     http://www.gknw.net/mirror/openldap/

   - optional recent Novell CLDAP SDK available from:

     http://developer.novell.com/ndk/cldap.htm

   Cygwin

   ------

   Before running nmake define the OPENSSL_PATH environment variable with

   the root/base directory of OpenSSL, for example:

     set OPENSSL_PATH=c:\openssl-0.9.8d

     set OPENSSL_PATH=c:\openssl-0.9.8e

   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