Fix two memory leaks in the new code. (There's no point compressing

Fix two memory leaks in the new code. (There's no point compressing
the scrollback if you then leak away all the memory you saved!) One
of the leaks - by far the bigger of the two - was in my temporary
diagnostic function cc_check(), which is particularly embarrassing :-)

git-svn-id: svn://svn.tartarus.org/sgt/putty@4638 cda61777-01e9-0310-a592-d414129be87e