tableeditor: ensure all reload operations are properly processed
timeshift: improve rdwr locking to try and reduce stutters.
timeshift: increase play out buffer to reduce stutter due to disk IO.
docs: update documentation about icon caching.
Correct some mistkaes picked up by static analysis.

Thanks to seo for pointing these out.
dvb: ensure that we only create radio/tv services from SDT
dvr: remove bad LIST_REMOVE() call if entry has no channel
Fix #1588 - epg: forgot to check string bounds for epggrab channel name
Fix #1589 - only remove "unsafe" characters if configured to do so.
logging: add option to log to separate file, useful for debug.

This can be simpler than using log to syslog OR log to console for
reporting problems.
access: add new option to override all ACL

This can be quite useful for debug/testing, especially when using
configuration provided by a user (saves deleting ACL files).
dvb: add a bit more debug to NIT processing
Fix #1596 - some version of git don't like describe in subdir
Fix #1595 - fix typo in IPV6 check for debian init script
Fix #1591 - timeshift: fix mutex deadlock affecting on-demand mode.

Note: there is still an issue I've realised in that writer_flush() could
potentially result in a single packet being written out of order as two
threads have the potential to write. This isn't fatal and is probably
rare enough to ignore at this stage.
Merge branch 'master' of https://github.com/tvheadend/tvheadend