minor edits to imb refactor

prefer memset so adding new members doesn't cause uninitialized bugs.

Initialize imbuf options correctly (thanks Campbell)

Cleanup - rename.

Make imbuf flags 16 bits.

We can clean up and decrease flags a bit more now, but left changes
to the bare minimum.
Some flags such as OpenEXR compression are used in DNA as well (should
be fixed at some point)

Merge branch 'master' into temp_imbuf_types_refactor

Bring back missing IMAGIC magic number for header

This is the kind of issue that makes this patch necessary,
magic number was used as format type.

Cleanup: Append IB_FTYPE to all image file types.

Also:

* cleanup unused quicktime file format (it's a movie format, not an
image)
* correct two instances of assigning quality to flags
* Remove jpeg enum from flag definition

Imbuf types refactor

Clearly separate flags from quality in imbuf struct.
Quality stands for PNG compression or jpeg quality.

Also fixed a wrong compression instance in dynamic painting
and commpression setting not propagated when copying
ImBuf to ImageFormatData

Merge branch 'master' into temp_imbuf_types_refactor

Merge branch 'master' into temp_imbuf_types_refactor

Imbuf types refactor.

ImBuf types were getting stored as bitflags in a 32bit integer which had
already run out of space. Solved the problem by separating file type to
an ftype enum, and file specific options to foptions.

Now we have 2^32 image formats to support, hopefully won't run out any
time soon.

Patch is committed to branch for inclusion after release due to
increased volatility, which could result explosions, spikes, acid, lava
and signs with "bad" on them if included now.