Implement Mantis ticket 0003646.

Reduce the TagItem overhead.

Reduce heap allocator overhead.

Add nullptr check, and return early from glue_db_init_and_load().

Since Debian package 1:0.8.8.4-4, the pkg-config file does not contain
-I/usr/include/libmodplug anymore, and we need to add the
"libmodplug/" prefix to the #include line.

When playing finite http streams, e.g. something from soundcloud,
eventloop stalls after pausing writefunc. TimeoutMonitor is cancelled
by the time resume happens, so when enough data is consumed writefunc
is called only once. Calling InvalidateSockets() from
input_curl_resume() seems to fix the issue.

Previously, the pointer was moved to undefined memory.

Increment the "path" earlier.

This was building broken paths like "/home/foo/~/bar".  Bug found by
Maarten de Vries.

Use Path::FromUTF8() for the g_get_home_dir() return value instead of
assuming it's already FS charset.

For callers that already have a Tag instance.

Methods BeginAdd() and EndAdd() have been replaced by class
TagBuilder.

Obsoletes Tag::BeginAdd() and the complicated "bulk add" code.

This is not a C++ class and must not be copied.

Move to TagSettings.c and use C99 initializers.

Allow using the Tag.cxx library without the Config library.

Migrate the remaining callers to FatalError().

Replaces struct playlist_provider.

Use only ConfigData.hxx in plugin sources to reduce header
dependencies.