Add support for ALTER [ object ] IF EXISTS

Prevent NPE in IndexCondition.toString() that may arise from debugging

# Conflicts:
#	h2/src/main/org/h2/res/help.csv

Typo in mvstore file format example.

Also switching 5 and tree, assuming that effectively, page 2 is replaced with a link to page 5, my understanding of log structured storage.

Ignore database resources that are created while running tests