[libsigcplusplus] Docs: Fix some minor typos.

[Murray Cumming <murrayc src gnome org>]

commit 52fbcbd74e257cef048d1adaffac0d2fd02000b2
Author: Murray Cumming <murrayc murrayc com>
Date:   Fri Apr 29 09:21:11 2016 +0200

    Docs: Fix some minor typos.

 sigc++/adaptors/adaptor_trait.h |    2 +-
 sigc++/connection.h             |    2 +-
 sigc++/functors/slot_base.h     |    2 +-
 sigc++/signal_base.cc           |    2 +-
 4 files changed, 4 insertions(+), 4 deletions(-)
---
diff --git a/sigc++/adaptors/adaptor_trait.h b/sigc++/adaptors/adaptor_trait.h
index e585dd3..7a534e8 100644
--- a/sigc++/adaptors/adaptor_trait.h
+++ b/sigc++/adaptors/adaptor_trait.h
@@ -44,7 +44,7 @@
  * see that adaptors are implemented like they are because
  * there is no way to extract the return type and the argument
  * types from a functor type. Therefore, operator() is templated.
- * It's instatiated in slot_call#<>::operator() where the
+ * It's instantiated in slot_call#<>::operator() where the
  * argument types are known. The return type is finally determined
  * via the callof<> template - a tricky way to detect the return
  * type of a functor when the argument types are known. Martin.
diff --git a/sigc++/connection.h b/sigc++/connection.h
index 4624636..f70ac4b 100644
--- a/sigc++/connection.h
+++ b/sigc++/connection.h
@@ -24,7 +24,7 @@
 namespace sigc
 {
 
-/** Convinience class for safe disconnection.
+/** Convenience class for safe disconnection.
  * Iterators must not be used beyond the lifetime of the list
  * they work on. A connection object can be created from a
  * slot list iterator and may safely be used to disconnect
diff --git a/sigc++/functors/slot_base.h b/sigc++/functors/slot_base.h
index 317d080..02c3d50 100644
--- a/sigc++/functors/slot_base.h
+++ b/sigc++/functors/slot_base.h
@@ -336,7 +336,7 @@ public:
    */
   void set_parent(notifiable* parent, notifiable::func_destroy_notify cleanup) const noexcept;
 
-  /** Add a callback that is executed (notified) when the slot is detroyed.
+  /** Add a callback that is executed (notified) when the slot is destroyed.
    * This function is used internally by connection objects.
    * @param data Passed into func upon notification.
    * @param func Callback executed upon destruction of the object.
diff --git a/sigc++/signal_base.cc b/sigc++/signal_base.cc
index e0dade2..8081b2e 100644
--- a/sigc++/signal_base.cc
+++ b/sigc++/signal_base.cc
@@ -190,7 +190,7 @@ signal_impl::notify_self_and_iter_of_invalidated_slot(notifiable* d)
   }
   else
   {
-    // This is occuring during signal emission or slot erasure.
+    // This is occurring during signal emission or slot erasure.
     // => sweep() will be called from ~signal_impl_holder() after signal emission.
     // This is safer because we don't have to care about our
     // iterators in emit(), clear(), and erase().