tests/test-xdg.t

revlog: update pure nodecache start lookup offset on insertion

test-storage.py is failing in pure builds because the population of the node
cache isn't accounting for the new starting offset after a revlog insertion.

This commit updates the node cache start offset to account for insertions.

I'm not 100% convinced this is the ideal solution. But it works and seems
correct.

Differential Revision: https://phab.mercurial-scm.org/D4996

#if no-windows no-osx

  $ mkdir -p xdgconf/hg
  $ echo '[ui]' > xdgconf/hg/hgrc
  $ echo 'username = foobar' >> xdgconf/hg/hgrc
  $ XDG_CONFIG_HOME="`pwd`/xdgconf" ; export XDG_CONFIG_HOME
  $ unset HGRCPATH
  $ hg config ui.username 2>/dev/null
  foobar

#endif