Avoid memory leaks when handling metadata strings

Don't duplicate strings when retrieveing metadata from media
files. As any requests for metadata strings would pass through
the binder, this would cause the reference to the duplicate string
to be lost, causing a memory leak as the duplicate would not be
freed.

Change-Id: I2593733472b1bb589bc502b2c11080f581015bb5
Bug fix for the MediaPlayer::prepare() api.

For an MP3 source, within the prepare command, ID3 tags are checked in search of
gapless playback info. This causes problems for streamed sources. If ID3v2 tags
aren't present, then a check is done for ID3v1 tags. This results in a read
command that asks the cache to jump to the end of the file, and subsequently
make an extra http call to request those bytes. For a streamed source, this
causes the file to not be downloaded automatically when MediaPlayer::prepare()
is called, and causes stuttering and extra buffering time to be needed when
start() is finally called.
The solution is to ignore the ID3v1 tags as the gapless info would never exist
there, and only check for ID3v2 tags.

Change-Id: I7d1b94cffbfe7c38ca094834dedbc92a58855e20
Memory leak solved in MPEG4Extractor::parseChunk for cover art

Repeated leaks detected in mediaserver context. Most chunks small but
some bigger. Adding up it was not uncommon to see 200Mb footprint.
libc memdebug allocation call stack showed the root cause in "covr"
parsing - that explains why content often was empty but sometimes big.

Change-Id: I0de6c1eeef174d2529973ff9c6a020ec3dd44c75
Fix bad checks that causes crash when streaming H.263 content.

Remove checks that causes crash for rtsp streamed h.263 content
with certain values in the RTP payload header:
Remove zero check for the five reserved bits in the payload header.
According to RFC 4629 these bits MUST be ignored by receivers.
Remove zero-check for the VRC (Video Redundancy Coding) bit,
skip packet instead.
Remove zero-check for the PLEN bits (extra picture header),
skip packet instead.
Remove zero-check for the PEBIT bits (extra picture header),
skip packet instead.
Remove corresponding zero check for the four resreved bits in the
AMR payload header. According to RFC 4867 these bits MUST be
ignored by receivers.

Change-Id: I7fc21d69a19d23da24f9267623c338d415ef1387