wmaker: make the '--replace' de-activable at compile time
As it is really unlikely that in normal use case someone would need this
feature, it is now conditional code, which is not enabled by default; the
configure scripts now propose a '--enable-wmreplace' option to enable the
corresponding code, as people making package for distributions may want to
enable the feature to provide users the ability to give a try of all the
window managers.
Suggested-by: Carlos R. Mafra <crmafra@gmail.com>
Signed-off-by: Christophe CURIS <christophe.curis@free.fr>