This commit fixes tagbar compatibility issues with the
[universal-ctags](/universal-ctags/ctags), which is the most active and
consistently updated fork of the old exuberant ctags.
Failing to suppress output can cause problems in some environments,
especially if the shell command fails or does something else spooky.
Example where failing to suppress the shell command causes issues with
[vim-airline](https://github.com/bling/vim-airline) with the tagbar
extension enabled:
Here's another example:
Both were taken using uxterm in Linux.
If the runtimepath has been set incorrectly and the autoload file is
getting loaded by something, then the code won't be able to load the
"plugin" file. Print a warning message and stop loading the file instead
of throwing lots of errors.
Instead of using 'echoerr' and essentially breaking the plugin after
that problems are now reported as warnings with 'echomsg'. They will
also only be shown once for a particular problem.
The current tagbar_autoclose state will be displayed in the statusline.
Also change the "hide nonpublic" flag to "v" to match the mapping and
properly document the statusline flags.
If someone already has a function that includes "JumpToTag" in its name
then the current method of detecting whether mappings should be
initialized would fail. Use a buffer-local variable instead.
If 'hidden' is not set then BufUnload is called every time a buffer
would get hidden, removing the fileinfo. This causes unnecessary ctags
processing of files.
