There is no abbreviation as such but you can remove the file/folder name or the avast context menu integration from being displayed by modifying the avast5.ini file.
Context (right click) Menu, very long file names how to change the display so as not to show the file names:
Using notepad, open the C:\Documents and Settings\All Users\Application Data\Avast Software\Avast\avast5.ini (XP file location)
C:\ProgramData\Avast Software\Avast\avast5.ini (Vista, Win7 file location)
Now find and edit the [UserInterface] section, add the new line after the label, ShellExtensionFileName=0 and save the file the avast self-defence will ask for confirmation. [UserInterface] ShellExtensionFileName=0
To Remove Shell Integration - use the ShellExtensionFileName=-1, to turn off the avast shell integration completely. (Note the value - minus 1)
Thank you for the modifier. Although my issue has been solved, I would still like to see forms of abbreviation implemented in future versions of Avast.
Perhaps if they concatenated the path, but I rather doubt it would be as easy to do that with a file name, where do you start as using the old 8.3 file name format would be pretty meaningless for a really really really long file name.