Two small patches for the isolationtester lexer

When writing an isolation testcase recently I bumped into the 1024 line buffer
size limit in the lexer for my setup block.  Adding some stored procedures to
the test makes it quite easy to break 1024 characters, and while these could be
added as steps it, it’s not a good workaround since the permutation order
becomes trickier (and more set in stone).  As far as I can see in the history,
this limit is chosen as a decent sized buffer and not rooted in a specific
requirement, so I propose to bump it slightly to 2048 instead (an equally
arbitrarily chosen number).  Is there a reason to keep it at 1024 that I’m
missing?

I also (again) forgot about the # comments not being allowed inside setup and
teardown blocks, so patch 0002 proposes adding support for these as the
documentation implies.  Since SQL comments will be counted towards the line
buffer, and sent with the command, supporting both kinds of comments seems
reasonable and consistent.

make check passes with these patches applies, but I’m quite rusty in this area
so I might be missing something.

cheers ./daniel