Refactor, replace deprecated setfsent() & C:o with setmntent()

The setfsent() family of APIs was never standardized and on Linux only
GLIBC implement them.  We've tried to overcome this limitation, and to
support uClibc/uClibc-ng and musl libc, by providing replacements APIs
in helpers.c.

However, and since we want to support alternative /etc/fstab files, the
setmntent() family of APIs is more widespread and supports reading from
any fstab or mtab file.

Signed-off-by: Joachim Wiberg <troglobit@gmail.com>

src/mount.c

@@ -23,7 +23,9 @@
 
 #include <errno.h>
 #include <string.h>
+#ifdef HAVE_MNTENT_H
 #include <mntent.h>
+#endif
 #include <sys/mount.h>
 
 #include "helpers.h"