filter-call: propagate modify value in filter() subexpressions

Whether a filter changes the message is a required information to
decide whether to clone a message when entering a log path. When
using the filter() expression within a filter, this information wasn't
properly propagated, which is fixed by this patch.

Signed-off-by: Balazs Scheidler <balazs.scheidler@balabit.com>
filter-re: backport filter_re_init() method from master

Signed-off-by: Balazs Scheidler <balazs.scheidler@balabit.com>
filter-re: fix match() filter initialization

This is a backported version of a fix in master simplified a lot for
backporting.

    The match() subexpression is a tweaked version of the generic FilterRE
    class, however the constructor didn't properly initialize the embedded
    FilterRE superclass. And the open coded version of the initialization
    lacked setting up the init virtual method, causing the modified flag
    not to be properly initialized in case store-matches was specified.

Signed-off-by: Balazs Scheidler <balazs.scheidler@balabit.com>
Merge pull request #252 from balabit/3.5/f/filter-abort-fix

3.5/f/filter abort fix