Newer versions of gcc have a small string optimizations that makes
moving FileRecordData objects behave incorrectly. When a small string is
moved, string_refs into it become invalid. Making a path on the fly
using the path() method also has the side effect of making
FileRecordData smaller in size.
Fixes a crash due to an assertion trying to access a
past-the-end iterator.
Gets content type detection to work, although only after
hashing is done (see comment in main.cpp for details).
Fixes a problem with the array passed to guess_content_type
being not sorted as the function expects.
Adds more assertions.
