The reason for the bug above is unclear but
- Modify pfs_upgrade so that it's result is easier to analyze in case something fails
- Fix several minor weaknesses which could cause that a successing test (either an
already existing or a to be developed one) fails because of imperfect cleanup,
too slow disconnected sessions etc.
should either fix the bug or reduce it's probability or at least
make the analysis of failures easier.
Before this fix, mysql_upgrade would always drop and re create
the performance_schema database.
This in theory could destroy user data created using 5.1 or older versions.
With this fix, mysql_upgrade checks the content of the
performance_schema database before droping it.
