gif2webp: simplify giflib version checking

introduce LOCAL_GIF_PREREQ/VERSION similar to the GCC variants in dsp.

Change-Id: I00ba5d523047b3b1c14ade992172e75e69043eb3
gif2webp: fix compile with giflib 5.1.0

DGifCloseFile() added an error code output parameter
http://giflib.sourceforge.net/gif_lib.html#compatibility

fixes issue #209

original patch by grizzly dot nyo at gmail

Change-Id: I5554de2bd70dbfd95fd356424ad5fb800ac94592
restore decode API compatibility

protect flip/alpha_dither w/a WEBP_DECODER_ABI_VERSION check

Change-Id: I437a5d5f78800f71b7e7e323faa321f946bf9515
restore encode API compatibility

protect WebPConfigLosslessPreset/WebPMemoryWriterClear w/a
WEBP_ENCODER_ABI_VERSION check

Change-Id: If4debc15fee172a3f18079bc2bd29eb8447bc14b
Merge changes If4debc15,I437a5d5f into 0.4.1

* changes:
  restore encode API compatibility
  restore decode API compatibility
remove the !WEBP_REFERENCE_IMPLEMENTATION tweak in Put8x8uv

There's no speed diff, so better remove it altogether

Reported in https://code.google.com/p/webp/issues/detail?id=215

Change-Id: I991330de18bec340029d6df5fed0dfb4337e4662
restore mux API compatibility

protect WebPMuxSetCanvasSize w/a WEBP_MUX_ABI_VERSION check

Change-Id: I6b01af55ebb4cc4c860d3cbf43be722077896748
Merge "restore mux API compatibility" into 0.4.1
bump version to 0.4.1

libwebp{,decoder} - 0.4.1
libwebp libtool - 5.1.0
libwebpdecoder libtool - 1.1.0

mux/demux - 0.2.1
libtool - 1.1.0

Change-Id: If593a198f802fd68c7dbbdbe0fc2612dbc44e2df
update AUTHORS

Change-Id: I1eae9342df7bf4e8e98d5328b2e3eab7cba9fee8
Merge "update AUTHORS" into 0.4.1
update NEWS for the next release

Change-Id: If708c6b442816f43522b7e5b292f3cba266d614a
remove -noalphadither option from README/vwebp.1

+ vwebp's -help output

this is a future option; missed in:
793368e restore decode API compatibility

Change-Id: If920df2cf8de57ebad93a6b98830562149396d8d
gif2webp: dust up the help message

* try to avoid trailing '.'
* rationalize capitalization

missed in:
0a8b886 dust up the help message

Change-Id: I6f80736cc8a2ff4f185f63d463a57d5bbf88a0db
Merge "update NEWS for the next release" into 0.4.1