Update Makefiles for out-of-source builds

Out-of-source build in <jabberd2_source>/obj-build
is done like this:

#> cd <jabberd2_source>
#> mkdir obj-build
#> cd obj-build
#> ../configure <args>
#> make
Merge pull request #23 from eagafonov/master

Initial commit for out-of-source builds