:swapname prints different string at different occasions

[GoogleCodeExporter]

What steps will reproduce the problem?

1. % vim -u NONE -U NONE --noplugin
2. :edit a_file.txt
3. :swapname           -> prints ".a_file.txt.swp"
4. :q!
5. % vim -u NONE -U NONE --noplugin a_file.txt
6. :swapname           -> prints "/home/user/.a_file.txt.swp"


What is the expected output? What do you see instead?

Prints the path of the swapfile as relative or absolute path, depending on when 
I called the command. Since I use the output in a script, it would be nice if 
the output would be consistent.

What version of the product are you using? On what operating system?

Both Vim 7.2 and Vim 7.4 on Linux.

Original issue reported on code.google.com by istjanic...@gmail.com on 23 Apr 2015 at 1:06