Make the scroller more "weighted" (or hard-to-drag) while you drag it

 Make the scroller more "weighted" (or hard-to-drag) while you drag it
 out of bounds, that is when the content is finished. In this way
 the user note that the content is at the end.

 All the others finger-scroll implementation (iphone,android) works this way ;)

 This is configurable by the 'thumbscroll_border_friction' config value,
 and by the 'ELM_THUMBSCROLL_BORDER_FRICTION' var.
 0.0 means: disable the friction
 0.5 is the default
 1.0 means: maximum friction

 I have tested this with every scroller in elm_test and seems to work
 well in all the occurence, if you see somthing strange in some scroller
 please let me know.

 DaveMDS

SVN revision: 54170