Added option to make dependencies optional.

- Closes #384
 - Users can set `g:vundle_no_deps` to disable dependency support if
   they want to.

autoload/vundle/config.vim

@@ -19,13 +19,15 @@ func! vundle#config#bundle(arg, ...)
     call s:rtp_add_defaults()
   endif
 
-  let deps = vundle#scripts#getdeps(bundle)
-  if !empty(deps)
-    for dependency in deps
-      if !has_key(g:bundle_names, dependency)
-        call vundle#config#bundle(dependency)
-      endif
-    endfor
+  if !exists('g:vundle_no_deps') || !g:vundle_no_deps
+    let deps = vundle#scripts#getdeps(bundle)
+    if !empty(deps)
+      for dependency in deps
+        if !has_key(g:bundle_names, dependency)
+          call vundle#config#bundle(dependency)
+        endif
+      endfor
+    endif
   endif
 
   return bundle

autoload/vundle/installer.vim

@@ -443,16 +443,18 @@ func! s:sync(bang, bundle) abort
     return 'error'
   end
 
-  let deps = vundle#scripts#getdeps(a:bundle)
-  if !empty(deps)
-    for dependency in deps
-      if !has_key(g:bundle_names, dependency)
-        let newbundle = vundle#config#bundle(dependency)
-        if (s:sync(a:bang, newbundle) == 'error')
-          return 'error'
+  if !exists('g:vundle_no_deps') || !g:vundle_no_deps
+    let deps = vundle#scripts#getdeps(a:bundle)
+    if !empty(deps)
+      for dependency in deps
+        if !has_key(g:bundle_names, dependency)
+          let newbundle = vundle#config#bundle(dependency)
+          if (s:sync(a:bang, newbundle) == 'error')
+            return 'error'
+          endif
         endif
-      endif
-    endfor
+      endfor
+    endif
   endif
 
   if empty(initial_sha)