serve: Make the server find assets generated by external tools. When a processor is bypassing PieCrust's pipeline, we don't know what output files they have produced, so if we don't find an asset in the record for a given path, we quickly check the output folder for any matching file there. If there is, just return it.

colorama==0.3.1
compressinja==0.0.2
Jinja2==2.7.3
Markdown==2.4.1
MarkupSafe==0.23
mock==1.0.1
py==1.4.23
Pygments==1.6
pystache==0.5.4
pytest==2.6.1
pytest-mock==0.2.0
python-dateutil==2.2
PyYAML==3.11
regex==2014.12.24
repoze.lru==0.6
six==1.7.3
smartypants==1.8.6
strict-rfc3339==0.4
textile==2.2.1
Werkzeug==0.9.6