#1098749: re-word gettext docs to not encourage using pygettext so much.

Also, add a link to the Babel package.
#19449: Handle non-string keys when generating 'fieldnames' error.

csv was handling non-string keys fine except for the error message
generated when a non-string key was not in 'fieldnames'.

Fix by Tomas Grahn, full patch-with-test by Vajrasky Kok (tweaked slightly).
Add workaround for VS 2010 nmake clean issue. VS 2010 doesn't set up PATH for nmake.exe correctly.
configure: echo message to AS_MESSAGE_FD. --silent redirects fd to /dev/null.