Vim-rtags does not update unsaved files for recent versions of rtags

[mvilim]

It appears that the vim-rtags unsaved-file feature does not work any more due to upstream changes in rtags.

1. it appears the --wait is flag is necessary for the reindexing of the unsaved file to complete before we attempt to run rc (otherwise we will attempt to e.g. jump to a symbol based on the old file contents). I expect that change occurred in this commit: Andersbakken/rtags@49494fe

2. the --unsaved-file path is no longer resolved from the relative path. This was changed here: Andersbakken/rtags@a35b093 It's possible that change was not necessary (I will open an upstream ticket to check), but in the meantime, I don't see a disadvantage to switching to passing absolute paths into unsaved file reindexing.

I will open a pull request with these changes.