dylink_import_module_symbols under repyportability violates Python import override conventions

[choksi81]

When doing from repyportability import * and add_dy_support(locals()) to add Repy and dylink calls to a Python program, dylink_import_module_symbols no longer respects the usual overriding conventions. Specifically,

# Import a variable ``foo''
dy_import_module_symbols("examplelib.repy")

# Override it locally
foo = "local override"

# Importing it again should reset foo to the library's version
dy_import_module_symbols("examplelib.repy")

assert(foo != "local override")
# XXX Failed to reset!

I'll add six unit tests that document the Python / Python-with-repyportability / Repy behavior for "import x" / "from x import *" (and the corresponding dylink calls).

[choksi81]

Tests committed in r7355.

[choksi81]

Summarized results as of r7355:

• Python import doesn't override definitions from a previous import
• Python from X import * resets definitions to the library's
• dy_import_module doesn't override
• dy_import_module_symbols resets
• Repyportability + dy_import_module doesn't override
• Repyportability + dy_import_module_symbols doesn't reset although it should.