Support for full text search in multithreaded mode

we removed this a long time ago

# Conflicts:
#	h2/src/docsrc/html/changelog.html

required passing the Column down to Value#convertTo
Note that the test code in testscript.sql was pulled from maxenglander's
PR #572

typo in merge

and making them sort-of regular functions makes it easier to allow
overriding them

Charset collation

The charset collator allows sorting strings according to their binary representation in a given charset.

Refactor synonym implementation

Remove most of the abstract methods in AbstractTable. Instead add abstract resolve()/asTable() method, that return the backing table.

Issue#556 close connections in tests (at least in case of successful execution)

unfortunately can't enable this yet - I'm pretty sure the FileSystem
side is fine, but the MVStore obviously needs more sync points somewhere

update docs to match code

this limit applies to both 32 and 64-bit VMs

Issue#556 tst fix

Update synonym implementation

Issue#560 thread leak

Check for unsupported column types in PostgreSQL mode