make sharing to clipboard a feature that can be disabled

this is for users that want to eliminate dependences (e.g. libxcb).
the feature is enabled by default and must be explicitly disabled.

fixes #84

src/ui/contextmenu.rs

@@ -4,6 +4,7 @@ use cursive::view::ViewWrapper;
 use cursive::views::{Dialog, SelectView};
 use cursive::Cursive;
 
+#[cfg(feature = "share_clipboard")]
 use clipboard::{ClipboardContext, ClipboardProvider};
 use library::Library;
 use queue::Queue;
@@ -30,6 +31,7 @@ impl ContextMenu {
             content.add_item("Show album", ContextMenuAction::ShowItem(Box::new(a)));
         }
         if let Some(url) = item.share_url() {
+            #[cfg(feature = "share_clipboard")]
             content.add_item("Share", ContextMenuAction::ShareUrl(url));
         }
 
@@ -45,9 +47,12 @@ impl ContextMenu {
                     }
                 }
                 ContextMenuAction::ShareUrl(url) => {
-                    ClipboardProvider::new()
-                        .and_then(|mut ctx: ClipboardContext| ctx.set_contents(url.to_string()))
-                        .ok();
+                    #[cfg(feature = "share_clipboard")]
+                    {
+                        ClipboardProvider::new()
+                            .and_then(|mut ctx: ClipboardContext| ctx.set_contents(url.to_string()))
+                            .ok();
+                    }
                 }
             });
         });

src/ui/listview.rs

@@ -9,6 +9,7 @@ use cursive::view::ScrollBase;
 use cursive::{Cursive, Printer, Rect, Vec2};
 use unicode_width::UnicodeWidthStr;
 
+#[cfg(feature = "share_clipboard")]
 use clipboard::{ClipboardContext, ClipboardProvider};
 use command::{Command, GotoMode, MoveMode, TargetMode};
 use commands::CommandResult;
@@ -321,6 +322,7 @@ impl<I: ListItem + Clone> ViewExt for ListView<I> {
                 };
 
                 if let Some(url) = url {
+                    #[cfg(feature = "share_clipboard")]
                     ClipboardProvider::new()
                         .and_then(|mut ctx: ClipboardContext| ctx.set_contents(url))
                         .ok();