configure: fix python install path

Pass the installation prefix to python.

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
configure: Fix quoting [CORRECTIVE]
Fix type to match expectation of ben_{list|dict}_for_each() [PREVENTIVE]
libbencode: Type safety-check for list and dict macro iterators [PREVENTIVE]

NULL dereference occurs if inappropriate type is passed for the iterator macro.
Document ben_free(NULL) behavior [DOCUMENTATION]
configure/Makefile.in: Implement configurable Python interpreter and C compiler [PERFECTIVE]

Note, --home makes Python installer to install Python at user's local packages
inside $HOME directory (e.g. $HOME/.local/lib/pythonXXX/site-packages/).
Clean up code [CLEANUP], document ben_list_for_each() [DOCUMENTATION]
Document ben_free() [DOCUMENTATION]
Merge pull request #1 from heikkiorsila/master

Update to Heikki's head