GuardLogStatement: small docs fixes
Redesign GuardLogStatement:
Turns out that the implementation based on the one published by Heiko Rupp
could simply not catch all the case in our test suite. I therefore opted to
backport the previous implementation - a simple Xpath rule, from GuardDebugLogStmt
into a java class.
Performance are not as good as the one based on Heiko's proposal, but it still
twice faster as the simple GuardDebogLogStmt (instead of five times faster). However,
correctness is in this case more important.