Fix crash when accepting change

The problem is the use of cursor movement methods to update cursor.
Cursor::forwardPos() steps into insets, which is not always what we
want. The problem here is that there is a math inset just after the
accepted change, and that the cursor steps into it for some reason.

This code is a nightmare anyway.

Fixes: bug #9145
sk.po: erroneous formats in strings
Fix bug #9146.

If LyX does not know about a given file format, it may easily
happen that the format is recognized as "latex" and this causes
bug #9146. This patch limits the check for a latex format to
non-binary files. The strategy for deciding that a file has
binary content is the same as that adopted by the "less" program.
Fix bug #9151 (Wrong reverse search for images and tables).

If the reverse position corresponds to an inset, its paragraph id
does not follow the main text numbering. Typically, an inset has
only a few paragraph, so that we would jump near the beginning of
the document. In this way we at least jump at the beginning of the
inset.