ulatency tree: fix when requested or default hierarchy is unavailable

- print human readable error if there is no cgroup hierarchy available
- print human readable error if the requested hierarchy is unavailable
- if no hierarchy was specified and the default one (cpu) is
unavailable, select first available

Fixes issue #44
ulatency.match_flag(): do not return inherited flags by default

add "recursive" parameter to override
fix timestamp handling in DBUS setActive and setActiveWithUser handlers
a bit optimize process_new()
Merge branch 'master' into devel
fix u_flag_clear_*() bug introduced in a8ecfe that tried to fix b0e7b10
make sure that only one iterate() is scheduled

wrappers around g_timeout_add_*(..., iterate,...):

gboolean iteration_request_full(gint priority, guint milliseconds, gboolean force);
gboolean iteration_request_seconds_full(gint priority, guint seconds);

shortcuts:

gboolean iteration_request(guint milliseconds);
gboolean iteration_request_seconds(guint seconds);

Use these to request new iteration rather than calling
g_timoute_add_*() directly. Each request will replace the previous
one, unless the previous one was 'forced'.

If you request forced iteration, further request will be dropped until
the forced one is dispatched.

As a bonus:
- first iteration is not delayed
- iteration interval can be changed now (iteration_interval global
variable)
fix u_session.X11Device was filled with X11Display
o-s-d mappings: fix possible failure with proc without cmdline
simplerules: add rules_files and rules_dirs configuration options
fix make test

to not fail due conflicting conf/ulatencyd.conf and simplerules