Support for multline/align (patch)

[Dekel Tsur]

The following patch adds support for the ams environments multline and align.
Currently, only align with one alignment point is supported, but
this should be hard to change.
To add an align/multline, insert a display formula, and do 'M-x break-line 1'
or 'M-x break-line 2'.
Please check if the changes I made doesn't break anything.

patch.gz