Fix processing of incomplete escapes in commands

The unescape() function used to go past the end of a string.

Thanks to Denis Protivenskiy.
Note wrong escape sequences fix in the ChangeLog
Merge branch 'fix-wrong-escape-sequences-crash'
Minor documentation updates
Update NEWS file
Version v0.7.5-beta
Bump version in configure script on *nix
Merge branch 'beta-0.7.5'