This adds support for gitignore-like wildcards and exclude patters in
reverse mode. It (somewhat) fixes#273: no regexp support, but the
syntax should be powerful enough to satisfy most needs.
Also, since adding a lot of --exclude options can be tedious, it adds
the --exclude-from option to read patterns from a file (or files).
This fixes a few issues I have found reviewing the code:
1) Limit the amount of data ReadLongName() will read. Previously,
you could send gocryptfs into out-of-memory by symlinking
gocryptfs.diriv to /dev/zero.
2) Handle the empty input case in unPad16() by returning an
error. Previously, it would panic with an out-of-bounds array
read. It is unclear to me if this could actually be triggered.
3) Reject empty names after base64-decoding in DecryptName().
An empty name crashes emeCipher.Decrypt().
It is unclear to me if B64.DecodeString() can actually return
a non-error empty result, but let's guard against it anyway.
Version 1.1 of the EME package (github.com/rfjakob/eme) added
a more convenient interface. Use it.
Note that you have to upgrade your EME package (go get -u)!
unPad16 returns detailed errors including the position of the
incorrect bytes. Kill a possible padding oracle by lumping
everything into a generic error.
The detailed error is only logged if debug is active.
