if a single text file name is supplied as argument
(e.g.: 'webpmux my_long_list_of_frames.txt'), the command
line arguments are actually parsed from this file.
Tokenizer will remove space, tabs, LF, CR, returns, etc.
+ changed ImgIoUtilReadFile() to return a null-terminated
data, for convenience.
+ misc clean-up in the code
BUG=webp:355
Change-Id: I76796305641d660933de5881763d723006712fa9
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a7f93fe32d