Shadow doesn't build in directories with whitespace, quotes, colons, or semicolons

[stevenengler]

If you build shadow in a directory path containing any of the following characters (and maybe others), shadow will fail to build:

• space
• tab
• linebreak (any of '\r', '\n', '\r\n')
• single quote
• double quote
• colon
• semicolon

We should fix this, at least for reasonable characters like spaces and colons.

On the other hand, shadow can't be run if the binary (and therefore the preload libs) exists in a directory path containing spaces or colons since these are path separators for LD_PRELOAD. But even if shadow can't run in these directories, it doesn't mean it should fail to build in these directories with confusing error messages.