Fix for bad host code generation for CTarget and more cleanup

Sorry for the continued minor updates (hopefully this will be the last of them!)

This PR does two things:

1. Only return a (non-DummyHost) CASTBuilder in the ExecutableCTarget -- this fixes host-code being generated for targets it has no business in doing so, e.g., for the OpenCLTarget
2. Change get_function_definition in the CASTBuilder such that global temporaries are only included in the function definition for device code -- currently, it would place the same temporary in both host and device code leading to a compilation error -- to that end, I've included a test that checks for this.
3. Some more minor cleanup (6c7648ab, 2bc2dc14, 70dc2d63)

AFAIK, # 2 only affects CTarget, ExecutableCTarget and the ISPCTarget, as all other targets define their own get_function_definition -- and all of these should only define global temporaries once (at the first device program)

I think this is a reasonable update, but I'm just starting to feel more confident in my understanding of host-code generation, so please point out any better ways to do this or other issues!

Nick

changed title from Fix for bad host code generation to Fix for bad host code generation for CTarget

changed the description

added 1 commit

• b8dab6fa - py2.6 format fix

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added 1 commit

• 6c7648ab - use absolute package imports, as seems to be the norm in loopy

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changed title from Fix for bad host code generation for CTarget to WIP: Fix for bad host code generation for CTarget and more cleanup

added 2 commits

• 2bc2dc14 - unused
• 70dc2d63 - include code from editor

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changed title from WIP: Fix for bad host code generation for CTarget and more cleanup to Fix for bad host code generation for CTarget and more cleanup

changed the description

added 4 commits

• 70dc2d63...6fd7edf1 - 3 commits from branch inducer:master
• 5898b88a - Merge branch 'master' into 'c_execution'

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LGTM, thanks!

merged

mentioned in commit 7c3e8334