Encapsulate TransactionStore.store field in preparation to a move

encapsulate TransactionStore.store field in preparation to a move into a separate package  and susequent split

Make MVMap to operate in non-blocking fashion

generate less garbage for String substring+trim

# Conflicts:
#	h2/src/main/org/h2/mvstore/MVStore.java

Minor free space accointing changes

Remove unexpected check for column count in MergeUsing

# Conflicts:
#	h2/src/main/org/h2/mvstore/FreeSpaceBitSet.java
#	h2/src/main/org/h2/mvstore/MVStore.java

filestore.clear() added, verifyLastChunk() moved to make assertions happy

fix endless loop. Map's version now is the version at which map was last modified. Previously it just followed stroe's version, which is kind of useless.

Fix issues with BUILTIN_ALIAS_OVERRIDE=1