Eliminate one implicit std::string copy.

The Release Track Id uniquely identifies a recording on a release - that
is, even if a recording appears twice on a release (meaning that the
combination of recording and release id are not enough to figure out
which one it is), the release track id will allow differentiating the two.

The tag names are taken from
https://musicbrainz.org/doc/MusicBrainz_Picard/Tags/Mapping

Workaround for assertion failure in PrintUniqueTag().

Necessary for "final" on gcc 4.6.

Use milliseconds precision to reduce rounding errors.

Use milliseconds precision to reduce rounding errors.

The new class is pluggable, to prepare for gzipped database files.

For now, the TextFile class remains, and will be refactored away
later.

Eliminate support for partial reads.  The Linux kernel will never
return partial results, so this buffering was unnecessary.

For database plugins that don't use the UpdateService.

Enables using range-based "for".

Error message was 'too few arguments for "find"' because the "base"
constraint was not supported, and no other constraints remained.

Fixes potential crash.

Check for 0 in "device" and "inode" instead.

Remove the C list_head library and use type-safe C++ instead.