Add emulation of the FT2 pattern loop bug.

One of the most (in)famous FT2 bugs is the E60 bug: When E60 is used on
a pattern row x, the following pattern also starts from row x instead of
the beginning of the pattern. This can be avoided by placing a D00
pattern break on the last row of the pattern where E60 was used.

Described here: http://www.milkytracker.org/docs/MilkyTracker.html#fxE6x

Test tune:
http://api.modarchive.org/downloads.php?moduleid=55647#roadblas.xm
Merge pull request #21 from eltoder/ft2-pattern-loop-bug

Add emulation of the FT2 pattern loop bug.