tools: Extend gpg-check-pattern.

* tools/gpg-check-pattern.c: Major rewrite.

Here is a simple pattern file:

1. Pattern to reject passwords which do not comply to
2. - at least 1 uppercase letter
3. - at least 1 lowercase letter
4. - at least one number
5. - at least one special character
6. and a few extra things to show the reject mode

Reject is the default mode, ignore case is the default

#[reject]
#[icase]

If the password starts with "foo" (case insensitive) it is rejected.

/foo.*/

[case]

If the password starts with "bar" (case sensitive) it is rejected.

/bar.*/

1. Switch to accept mode: Only if all patterns up to the next "accept"
2. or "reject" tag or EOF match, the password is accepted. Otherwise
3. the password is rejected.

[accept]

/[A-Z]+/
/[a-z]+/
/[0-9]+/

/[^A-Za-z0-9]+/

Someone™ please write regression tests.

• Signed-off-by: Werner Koch <wk@gnupg.org>