Fix configure dirs

Fix configure dirs

Fix overridable configure directories, namely, --bindir, --sbindir,
and --mandir.

Variables 'bindir', 'sbindir', and 'mandir' are exported from
'configure.ac' to 'Makefile.am'. At first, it would seem to be
possible to do the following:

  MANDIR := $(mandir)
  ...
  mandir = $(versionedsharedir)$(datarootdir)/$(MANDIR)

However, this does not work in the output of 'configure' (i.e., the
'Makefile'), these variables will be reordered:

  mandir = $(versionedsharedir)$(datarootdir)/$(MANDIR)
  ...
  MANDIR := $(mandir)

As a result, 'MANDIR' will capture not the exported value from
'configure.ac' but the 'mandir' defined in the 'Makefile'.

The solution is explicitly export these variables from 'configure.ac'
with different names, namely, 'BINDIR', 'SBINDIR', and 'MANDIR':

  AC_SUBST([BINDIR], $bindir)
  AC_SUBST([SBINDIR], $sbindir)
  AC_SUBST([MANDIR], $mandir)

The rest is just fixing the paths and the symlinks in the 'Makefile'.

Signed-off-by: Jose A. Lopes <jabolopes@google.com>
Reviewed-by: Klaus Aehlig <aehlig@google.com>