ismindex: produce .ismf file

This is a non-standard file that maps the MSS segment names to offsets
in the ISMV file. This can be used to build a custom MSS streaming
server without splitting the ISMV into separate files.

Signed-off-by: Martin Storsjö <martin@martin.st>
Merge commit 'b21e989a3c076d94cfdde0303724db841dd60cad'

* commit 'b21e989a3c076d94cfdde0303724db841dd60cad':
  ismindex: produce .ismf file

Conflicts:
	tools/ismindex.c

Merged-by: Michael Niedermayer <michaelni@gmx.at>
avfilter/x86/idet: fix license header (GPL -> LGPL)

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>