lib/omb-prompt-base: Set a timeout on the git command

The calculate of git_summary_status can be extremely expensive for
large repos. This results in the shell becoming unresponsive.

We now set a timeout of 0.2 seconds to make sure we always have a
responsive shell.

* lib/omb-prompt-base: Set a timeout on git commands
* lib/omb-prompt-base: Fix timeout bug
* lib/omb-prompt-base: Rename function "{run_with => _omb_prompt}_timeout"
* lib/omb-prompt-base(_omb_prompt_timeout): Fix coding style
* lib/omb-prompt-base(_omb_prompt_timeout): Check timeout commands on startup

Fixes #172
Co-authored-by: Koichi Murase <myoga.murase@gmail.com>

lib/omb-prompt-base.sh

@@ -43,6 +43,7 @@ SCM_GIT_BEHIND_CHAR="↓"
 SCM_GIT_UNTRACKED_CHAR="?:"
 SCM_GIT_UNSTAGED_CHAR="U:"
 SCM_GIT_STAGED_CHAR="S:"
+SCM_GIT_TIMEOUT="0.2"
 
 SCM_HG='hg'
 SCM_HG_CHAR='☿'
@@ -105,9 +106,27 @@ function _omb_prompt_format {
 }
 
 function _omb_prompt_git {
-  command git "$@"
+  _omb_prompt_timeout "$SCM_GIT_TIMEOUT" command git "$@"
 }
 
+## @fn _omb_prompt_timeout
+##   Runs the given command with the given timeout
+##   @param $1 Timeout in seconds
+##   @param $@ Command to be executed.
+if _omb_util_command_exists timeout; then
+  function _omb_prompt_timeout {
+    timeout "$@"
+  }
+elif _omb_util_command_exists gtimeout; then
+  function _omb_prompt_timeout {
+    gtimeout "$@"
+  }
+else
+  function _omb_prompt_timeout {
+    "${@:2}"
+  }
+fi
+
 function scm {
   if [[ "$SCM_CHECK" = false ]]; then SCM=$SCM_NONE
   elif [[ -f .git/HEAD ]]; then SCM=$SCM_GIT