Assorted minor changes

increase lock timeout to TestConcurrentUpdate due to Travis failures

In the REGEXP_REPLACE function, when in PostgreSQL compatibility mode, accept the 'g' flag.

Create local variable for whether we're in PostgreSQL mode, remove implementation details from doco, add compiler/IDE hint for falling-through switch statement

Add boolean flag to makeRegexpFlags that indicates whether the presence of a global flag should simply be ignored (i.e. when in PostreSQL mode) or whether it should throw an exception.

If the database is in PostgreSQL mode and the 'g' flag is not present, use the String.replaceFirst method instead of the H2 default String.replaceAll method when doing the regex replace.

In the REGEXP_REPLACE function, when in PostgreSQL compatibility mode, accept (but ignore/strip out) the 'g' flag.

fix doing sorted-insert mode in parallel where not wanted

Remove comparison from features.html and unused dependencies from pom.xml

Add support for SELECT FOR UPDATE with JOINs in MVStore mode

Speedup unused chunks collection

Add AsynchronousFileChannel-based experimental FilePathAsync

Tiny optimization: use `System.arraycopy` when possible

Export datetime value functions to SQL using standard syntax