* Validate the email filter by manipulating stdin. Additional checks for
all the arguments can be added in a later patch.
* Add the exec prefix to all informational messages.
* Rename the filter repository to filter-exec. The Git repository itself
is not renamed since it can be shared amongst all filter types.
* In the filter checks, check whether all arguments are passed properly
instead of validating the buffer/stdin only.
Signed-off-by: Lukas Fleischer <cgit@cryptocrack.de>
