pep8_tap: fix counter

In 1f796f06 I broke the issue counter. This fixes the breakage.
pep8_tap: Fix crash with invalid encoded source data
pep8_tap: ignore non-Python files
tap_tool_dispatcher: run all tools in parallel

Running the different *_tap tools in parallel allows for significant
speedups on our build server; a job with ~440 files took 1min35s
previously, and now takes < 30s to complete.
jenkins-debian-glue-buildenv-taptools: it's libperl-critic-perl, not perlcritic
pep8_tap: adjust Encoding handling for ruby1.8
pep8_tap: don't reenable default-disabled checkers

As explained in https://github.com/jcrocholl/pep8/issues/212, some checkers are disabled by default, as they only apply to old PEP8 versions. We shouldn't turn them on again.
Fix script name of pep8_tap

This was mistakenly renamed in commit 5d33d21b17ac83 AKA PR 105
pep8_tap: further fix for encoding issue with ruby1.8
Clarify Depends/Recommends of jenkins-debian-glue-buildenv-taptools
Release new version 0.10.0