Fix an array-size bug in modmul, and add some tests for it.


git-svn-id: svn://svn.tartarus.org/sgt/putty@9977 cda61777-01e9-0310-a592-d414129be87e
Add some missing bounds checks in signature verification routines.


git-svn-id: svn://svn.tartarus.org/sgt/putty@9978 cda61777-01e9-0310-a592-d414129be87e
Replace some 'sfree' calls of bignums with the proper 'freebn'.


git-svn-id: svn://svn.tartarus.org/sgt/putty@9979 cda61777-01e9-0310-a592-d414129be87e
Verify RSA keys created by rsa2_openssh_createkey.


git-svn-id: svn://svn.tartarus.org/sgt/putty@9980 cda61777-01e9-0310-a592-d414129be87e
Found a lot of places in sshbn.c where for-loops zeroing out memory
just before freeing it really ought to be smemclrs.


git-svn-id: svn://svn.tartarus.org/sgt/putty@9981 cda61777-01e9-0310-a592-d414129be87e
Raise the default scrollback from 200 to 2000 lines. The former was
not so silly in the 1990s and before I implemented scrollback
compression, but it's been a ridiculously low default for a while now.


git-svn-id: svn://svn.tartarus.org/sgt/putty@9982 cda61777-01e9-0310-a592-d414129be87e