Another big batch of memory leak fixes, again mostly on error paths.

Another big batch of memory leak fixes, again mostly on error paths.
The most interesting one is printer_add_enum, which I've modified to
take a char ** rather than a char * so that it can both realloc its
input buffer _and_ return NULL to indicate error.

git-svn-id: svn://svn.tartarus.org/sgt/putty@9959 cda61777-01e9-0310-a592-d414129be87e