[analyzer] scan-view: don't ever serve absolute paths.
[analyzer] scan-view: don't ever serve absolute paths.

At one point in time scan-view allowed absolute paths to reference files
within the server root, but this doesn't seem to be used anymore, and
caused problems if a server-root-relative path actually matched an
absolute path to an existing file. This patch just treats paths as
server-root-relative all the time.

PR15843

git-svn-id: ffe668792ed300d6c2daa1f6eba2e0aa28d7ec6c@180715 91177308-0d34-0410-b5e6-96231b3b80d8

llvm-mirror/clang,apple/swift-clang,apple/swift-clang,llvm-mirror/clang,apple/swift-clang,llvm-mirror/clang,apple/swift-clang,apple/swift-clang,llvm-mirror/clang,llvm-mirror/clang,llvm-mirror/clang,apple/swift-clang,llvm-mirror/clang,apple/swift-clang,apple/swift-clang,apple/swift-clang,llvm-mirror/clang,apple/swift-clang,llvm-mirror/clang,llvm-mirror/clang