This is a follow-up of bug #8967. The implementation is self-explaining, the
only part which needs a comment is lyx2lyx: Since a 100% correct solution is
not possible, it has been decided not to switch amsmath off in the forward
conversion if no other ams command than \smash[t] and \smash[b] is used, but
to consider it a bug that older versions do not load amsmath automatically for
these commands. In the backward direction it is easy to keep the document
compilable, so just do that.
LyX, lyx2lyx and tex2lyx produce now all the same version indicator consisting
only of the major and minor version. It is not decided yet whether future
development versions will add a -dev suffix, but for 2.1.0 this change fixes
the inconsistencies.
Unfortunately automake does not support file names with spaces for files in
EXTRA_DIST: These file names are put into a shell list, and it is impossible
quote the name in a way that works both with the shell and with make.
Therefore I removed the corresponding test file.
