servicemp3: remove unnecessary locking for subtitles.

It appears the code accessing the subtitles cache is run
all within one thread and the enigma2 timer mechanism is
non-preemptive.
esubtitle.cpp: cosmetics and small optimisations
esubtitle.cpp: honour "rewrap subtitles" option for "gstreamer" media
text subtitles
servicemp3: subtitles: reduce debugging output and remove an unused variable
Merge branch 'master' of git://git.code.sf.net/p/openpli/enigma2