Fix building without PAM

Fixes this error in `make`:

    /usr/bin/install: cannot stat ‘epam’: No such file or directory
    make[1]: *** [post-build] Error 1
Fix typo in configure help (`--disable-pam`)
Merge pull request #184 from weisslj/fix-build-without-pam

Fix building without PAM (and small typo in configure help)