make sure shell conditionals are properly formed

In the case that wget or curl don't exist, the `[ "$APP" = ... ]` code can turn out to be evaluated like `[ "none" =  ]`, owing to the order in which replacements are done in the shell.

By prefixing everything, the functionality is kept but the error condition is avoided.
Merge pull request #268 from deoxxa/patch-1

make sure shell conditionals are properly formed