Fixes to verification scripts, plus a bug in ProcSelfIO handler

1. Added code so that the verification scripts can test handlers
that deal with "/proc" files that are symlinks.

2. Added a "verify-all-handler" wrapper script that will find
all known handler classes and testing them.

3. The ProcSelfIO handlers mistakenly registered it's primary
data file as "/proc/net/io" when it's really "/proc/self/io".