improve file watching

By default, macs have 256 open files allowed by a given process.
This sucks when you end up with over 256 files modified in a repo
because after you've watched all of them, lots of other calls to
the command line will fail due to violating the limit.

Given there's no easy platform agnostic way to see what you've got
configured for how many files a process can have open, I'm going to
arbitrarily set the max to 200 and when we hit the limit we start
unwatching older files to make way for new ones.

WIP

pkg/gui/gui.go

@@ -15,7 +15,6 @@ import (
 	"strings"
 	"time"
 
-	"github.com/fsnotify/fsnotify"
 	"github.com/go-errors/errors"
 
 	// "strings"
@@ -82,7 +81,7 @@ type Gui struct {
 	statusManager *statusManager
 	credentials   credentials
 	waitForIntro  sync.WaitGroup
-	fileWatcher   *fsnotify.Watcher
+	fileWatcher   *fileWatcher
 }
 
 // for now the staging panel state, unlike the other panel states, is going to be
@@ -840,7 +839,7 @@ func (gui *Gui) RunWithSubprocesses() error {
 					}
 				}
 
-				gui.fileWatcher.Close()
+				gui.fileWatcher.Watcher.Close()
 
 				break
 			} else if err == gui.Errors.ErrSwitchRepo {