Fix incorrect access of context for -Dvar definitions.
When a variable is defined in the command line using '-Dvar', an exception occurs. This is because the code accesses the context dictionary using the 'name' variable instead of the 'value' variable.
Patch by Urs Fleisch to fix under Python 3.2.
From Emacs 22, interactive-p is deprecated, and now raises a warning. Reported by Leo Liu.
…dead buffer. Reported by Leo Liu.
…Python3. Reported by Patrik Hartlén and (?) ufleisch.
This is to provide more helpful message when, for example, pymacs-loading a python module and one of its dependencies is missing.