Added a TODO
Revamped the way MD5 checksums are verified

Now the md5_verify() function supports having several different
CHECKSUMS.md5 files, as is the way with Slackware.

For example:
ftp://ftp.slackware.com/pub/slackware/slackware-14.0/CHECKSUMS.md5
ftp://ftp.slackware.com/pub/slackware/slackware-14.0/patches/CHECKSUMS.md5

The "downside" is that we now do the PGP verification each time, instead
of using the $CHECKSUMS_VERIFIED variable.

Of course this is better for security anyway, but the swsp output tends
to get a bit cluttered with all the verifications.

This reminds me, that I need to evaluate and think through the possible race conditions
with all the file verifications anyway.
Added update and verification of ChangeLog.txt to list_updates()
Added update and verification of ChangeLog.txt to print_patch_stats()

Also re-arranged the local variable initializations.
Removed commented $ARCH stuff

We use $MACHTYPE to determine the architecture, which is Bash's builtin
variable.
Created print_patch_details_from_changelog() and removed dupe code

Oops! Had the same snippet in three different places :P
tgz -> t[gx]z
Removed unnecessary variable

This relates to print_patch_details_from_changelog().