Fix transaction nesting caused by LocalFile.

Fix transaction nesting caused by LocalFile.

The transaction bracket in LocalFile::recordUpload2 used to span a call
to WikiPage::doEdit, which in turn opens a transaction. Nesting transactions
this way does not work: the first transaction is committed prematurely when
the second one starts. This may cause serious database corruption and
generally exciting behavior.

This change commits LocalFile's own transaction before any interaction
with WikiPage. There may be a race condition here, but that case seems to
be already handled in the code. Also, in the previous "broken" state, all
transactional protection got lost anyway - so this should at least be no
worse than what we had.

This may be changed back if and when we have support for nested
transactions.

Change-Id: I20d90fedb2d19c64ccf0f3942ddda756fe511c12