Fixed `fish-shell` support bugs, and removed unnecessary hash commands.

Signed-off-by: Rack Lin <racklin@gmail.com>
Fixed search for apxs2 binary
Merge pull request #426 from racklin/bugfix/fish-shell1

Fixed `fish-shell` support bugs, and removed unnecessary hash commands.
Some comments and extra debug info
Merge pull request #427 from morozov/apxs

Fixed search for apxs2 binary
Runs make clean before installing an extension.