More robust templating (#1157)

Don't require $source and $dest to be bare tokens.
Fix convert tests

Use some shell trickery to get the pipelined command to work.
Added option --pretend to only print the filenames of files to import without importing them
Fix 2.6 compatibility with subprocess

We can add this back once we go 2.7-only.
embedart: Added syspath call to art exists check
Reduced the count of accesses of the pretend config option. Now it's only one place where it is read.
Changed the output to use the log system rather than print_.
The last commit broke the tests. Repaired...
Merge pull request #1163 from mluds/embedart-windows-fix

embedart: Windows fix
Changelog for #1163
Implemented a better solution for the pretend flag
Corrected the documentation (shortcut -e is not available any more)
Merge pull request #1162 from mried/import-pretend

Added option --pretend to only print the filenames
Changelog and rewording for import --pretend

(#1162)