Our test suite did not reset the config directory for each test class as
it does for the data directory. In addition it copied all files from the
main config directory over. Both may create an unpredictable state for
tests.

This streamlines the initialization.

This fixes the problem that $PARSER_MODES was sometimes unset by PHPUnit
between test functions that called p_get_parsermodes() as PHPUnit tried
to restore the global environment. I couldn't reproduce this when I
executed all tests but just when I executed a single plugin test.

https://github.com/splitbrain/dokuwiki/pull/96#issuecomment-5195756

There's still more that I'd like to moved out. bootstrap should not
contain any logic but only call the appropriate functions for setup the
test environment.

This should make it much easier to do integration tests based on the new
TestRequest utility.

verify that multiple requests can be made with multiple test methods.