Various fixes...

initialize ex_pathlen to -1 so it isn't checked if pathlen
is not present.

set ucert to NULL in apps/pkcs12.c otherwise it gets freed
twice.

remove extraneous '\r' in MIME encoder.

Allow a NULL to be passed to X509_gmtime_adj()


Make PKCS#7 code use definite length encoding rather then
the indefinite stuff it used previously.