#13 configure does not like building in a different dir

[Hubert Figuière]

I always build in a different directory than the source
dir ($top_src). XPLC does not support that.

If I do
../../xplc/configure
Then I don't have any makefiles.

[Pierre Phaneuf]

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user_id=5633

True. I should work on this feature, but it is not very high
priority at the moment (I do not want to waste too much time
fiddling with the build system, rather than work on XPLC
itself).