#45 Rewind feature to GTK version

[Juha Laukkanen]

This patch adds rewind feature to GTK version. There are two config params:

rewind_count_max => how many blocks are reserved maximum, higher value leads to greater memory usage naturally but longer rewind log
rewind_interval => default interval is 165ms and higher value leads to more inaccurate rewind but longer rewind log

The patch also fixes
memtell() telling incorrect size because data is not flushed.
wxWidgets front end having too small buffer for rewinds resulting overflows.

Patch in src level.

[skid]

Committed as svn 1438