Fix issue with bad completions when backspacing

By default, Vim chooses to perform its own filtering of the items in the
completion menu when the user presses backspace or C-H if the menu is
already shown. We need to disabuse Vim of the notion that it knows what it's
doing and to let us handle it.

Fixes #526.
Remove clang_includes folder
Don't pass extra include path to libclang
CSharp GoTo was off by one column and line
Merge pull request #917 from mispencer/CsGotoOffOneLineColumn

CSharp GoTo is off by one column and line
Detach from controlling terminal to avoid receiving SIGINT.
Add libclang builtin headers for LLVM release 3.3 and 3.4

Copied from the ./lib/clang/3.X/include directories of the prebuilt binary releases at llvm.org, specifically
http://llvm.org/releases/3.3/clang+llvm-3.3-amd64-Ubuntu-12.04.2.tar.gz and http://llvm.org/releases/3.4/clang+llvm-3.4-x86_64-linux-gnu-ubuntu-13.10.tar.xz.

These headers don't appear to be arch dependent, so we should be good.
Add builtin includes for AppleClang 5.1

Copied from Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/lib
Use OnWindows from utils instead of ad-hoc platform check.
Merge pull request #918 from m4burns/master

Detach from controlling terminal to avoid receiving SIGINT.
Merge pull request #910 from nickhutchinson/fix-libclang-includes

Fix libclang's #include search path
More strongly condemn use of system libclang
Revert "Add builtin includes for AppleClang 5.1"

This reverts commit c62bb98f4f4ca52fcb765bb81b526ceb433ae157.
Revert "Add libclang builtin headers for LLVM release 3.3 and 3.4"

This reverts commit 2f84503a99bc1be474719d42ffdc42e5d0de215b.
Revert "Don't pass extra include path to libclang"

This reverts commit 7bdff8941c1bcb8df3badbef403927211cb3391a.
Revert "Remove clang_includes folder"

This reverts commit cca4785fb69740f36b6d07280d2fb4d6dc039e62.
Merge remote-tracking branch 'upstream/dev'
Merge remote-tracking branch 'upstream/master'