This threads SectionName through the allocateCodeSection/allocateDataSection APIs, both in C++ and C land.
It's useful for the memory managers that are allocating a section to know what the name of the section is.
At a minimum, this is useful for low-level debugging - it's customary for JITs to be able to tell you what
memory they allocated, and as part of any such dump, they should be able to tell you some meta-data about
what each allocation is for.  This allows clients that supply their own memory managers to do this.
Additionally, we also envision the SectionName being useful for passing meta-data from within LLVM to an LLVM
client.

This changes both the C and C++ APIs, and all of the clients of those APIs within LLVM.  I'm assuming that
it's safe to change the C++ API because that API is allowed to change.  I'm assuming that it's safe to change
the C API because we haven't shipped the API in a release yet (LLVM 3.3 doesn't include the MCJIT memory
management C API).