Auto merge of #1959 - lucab:lucab/skip-dotdir, r=alexcrichton

Cargo recursively looks for TOML manifest into child directories,
sometimes getting into unrelated files when exploring hidden
directories (eg. quilt .pc).

This commit lets cargo skip dot directories, to partially avoid
the issues described in #1423.

Signed-off-by: Luca Bruno <lucab@debian.org>