which.js: root is allowed to execute files owned by anyone

When running in say, a chroot enviornment, the process UID and GID will be 0, but the files in the system (like /usr/bin/git) may not be owned by root itself.

This patch modifies the isExe function that tries to determine if a process is executable and allows root to execute any file that has any executable bit set, instead of just allowing it if the other executable bit is set.