[libsigcplusplus] C++11: slot: Use = default for simple copy constructor.

[Murray Cumming <murrayc src gnome org>]

commit 20e91aa4f5374cfa01698caea8ac83c380befea2
Author: Murray Cumming <murrayc murrayc com>
Date:   Fri Apr 1 18:45:17 2016 +0200

    C++11: slot: Use = default for simple copy constructor.
    
    With help from clang-tidy, like so:
    clang-tidy-3.8 -fix --checks=modernize-use-default --header-filter=.*  `find . -name "*.cc"`
    after using "bear make all check".

 sigc++/functors/slot.h |    7 ++-----
 1 files changed, 2 insertions(+), 5 deletions(-)
---
diff --git a/sigc++/functors/slot.h b/sigc++/functors/slot.h
index f186ba8..91b42cd 100644
--- a/sigc++/functors/slot.h
+++ b/sigc++/functors/slot.h
@@ -193,7 +193,7 @@ public:
   /** Constructs a slot, copying an existing one.
    * @param src The existing slot to copy.
    */
-  slot(const slot& src) : slot_base(src) {}
+  slot(const slot& src) = default;
 
   /** Constructs a slot, moving an existing one.
    * If @p src is connected to a parent (e.g. a signal), it is copied, not moved.
@@ -206,10 +206,7 @@ public:
    * @return @p this.
    */
   slot& operator=(const slot& src)
-  {
-    slot_base::operator=(src);
-    return *this;
-  }
+  = default;
 
   /** Overrides this slot, making a move from another slot.
    * If @p src is connected to a parent (e.g. a signal), it is copied, not moved.