This variable is being computed with an eval call which seems to be
upsetting the build bots but none of my systems. So use:
* cmd:python2 instead of cmd:python2.7 and lib:libpython2.7
* cmd:python3 instead of cmd:python3.6 and lib:libpython3.6m
devel:libpython was in BUILD_PREREQUIRES until the previous commit
and was moved to BUILD_REQUIRES. Move it back to BUILD_PREREQUIRES.
Every commit in this recipe has been tested locally on each arch,
but something went wrong with pycurl_x86 in the build servers.
A REVISION bump was not necessary because the resulting packages
are the same except that REQUIRES_python{,3} are now sorted. But
let's kick a rebuild, after all.
