[BUGFIX] Some methods in t3lib_TSparser should be static

A few methods in t3lib_TSparser are called statically but are not
declared as being static. This leads to PHP notices.

Change-Id: I7ea7cb659a830e74c4f8797f118662b517015614
Fixes: #30058
Releases: 4.6
Reviewed-on: http://review.typo3.org/5085
Reviewed-by: Xavier Perseguers
Tested-by: Xavier Perseguers