Work around quirky filenames in synctex.gz.

* lisp/pdf-sync.el (pdf-sync-correlate-pdf): Added workaround for
filename bug in synctex.
Uninstall correct function.

* lisp/pdf-tools.el (pdf-tools-uninstall): Remove the correct hook function.
Use stderr for warnings in synctex.

* src/synctex_parser.c: Defined printf to write to stderr.