Fixes deadlock on small responses.

Fixes a problem with the "curl" input plugin: IsEOF() always returns
true because the "open" flag was cleared by
CurlInputStream::RequestDone() when end-of-stream was reached.  This
flag stays false even when seeking to another position has succeeded.

This patch resets the "open" flag to true after seeking successfully.

Fixes -Winconsistent-missing-override (clang 3.6).

While seeking, metadata must not be updated.  ResponseBoundary() was
added in MPD 0.19.1, but I forgot to add the IsSeeking() check there.
This caused the "seekable" flag to reset.

Fixes crash in the "audiofile" decoder while logging the seek error.

Fixes playback of redirected streams.

Fixes truncated lines in m3u and cue files (regression by commit
67958f7f).

Fixes deadlock bug in the "mms" plugin.

Make the "open" method of plugins "file" and "archive" dummy methods
that always fail.  Instead, let InputStream::Open() hard-code access
to these two plugins by using OpenLocalInputStream().  This allows
simplifyin the algorithm for falling back to probing archive plugins.

Combines the "file" and the "archive" input plugins.

This special case was useless.  Fixes the dreaded "Unrecognized URI"
error message when a file does not exist.

The second time init was called, http_200_aliases pointed to a freed pointer
and leaded to a SEGFAULT.

Fixes hanging NFS client.

Necessary for "final" on gcc 4.6.

Reduce header dependencies.

Seeking on NFS or SMB is cheap.  Actually, only HTTP streams are
expensive to seek.  This enables a few features on NFS/SMB files, for
example Ogg tags.

Has been moved to class InputStream long ago.