[include-fixer] Keep dot dot in SymbolInfo file paths.

Summary:
Currently, removing dot dot in header's path doesn't make include-fixer
minimize path correctly in some cases, for example, specify a relative search
path based on the build directory("-I../include/").

Besides, removing dot dot can break symbolic link directories. So don't
removing it for now.

Reviewers: ioeric, bkramer

Subscribers: cfe-commits

Differential Revision: http://reviews.llvm.org/D21132

llvm-svn: 272152