Fix spelling in comments and documentation using codespell

Apply the utility from https://github.com/codespell-project/codespell/
to fix spelling issues in the headers under both include and interface
directories and add a file with a couple of exceptions.

The exact command line used was:

    $ codespell -w -I misc/scripts/codespell.ignore -i 3 in*

include/wx/private/fswatcher.h

@@ -62,7 +62,7 @@ public:
         if (!DoAdd(watch))
             return false;
 
-        // add watch to our map (always succeedes, checked above)
+        // add watch to our map (always succeeds, checked above)
         wxFSWatchEntries::value_type val(watch->GetPath(), watch);
         return m_watches.insert(val).second;
     }

include/wx/private/graphics.h

@@ -54,7 +54,7 @@ public :
        virtual void Set(wxDouble a=1.0, wxDouble b=0.0, wxDouble c=0.0, wxDouble d=1.0,
            wxDouble tx=0.0, wxDouble ty=0.0) = 0;
 
-       // gets the component valuess of the matrix
+       // gets the component values of the matrix
        virtual void Get(wxDouble* a=NULL, wxDouble* b=NULL,  wxDouble* c=NULL,
                         wxDouble* d=NULL, wxDouble* tx=NULL, wxDouble* ty=NULL) const = 0;
 

include/wx/private/window.h

@@ -76,7 +76,7 @@ public:
         }
 
         // Ensure that we return true the first time we're called,
-        // asuming that the value will always be set to a non-default value.
+        // assuming that the value will always be set to a non-default value.
         return m_value == T();
     }