NSArray properties should use copy semantics

…otherwise, arrays have a way of disappearing when the client code drops them, or changing if the client code passes an NSMutableArray.

• Changed sectionTitles and sectionImages properties to copy ownership.
	» Even though these are shallow array copies, I don't see any major issues (crashes) if a string or image were to change its content without notice.
• Fixed setSectionTitles: to copy the sectionTitles argument passed in.
	» It wasn't being retained before, crashing deallocated-instance crashes.  Now being copy'd.
Fixed retaining/releasing in SVSegmentedThumb setter methods

setBackgroundImage:, setTintColor:, setTextColor: and setTextShadowColor: were all missing retains for the newColors being passed in, and releases for the existing colors, as dictated by the strong ownership on their associated properties.  Fixed to work like synthesized strong setters.

• Added early-out checks to if the object passed in is the same as the existing one.  None of the additional operations in these setters need to happen if this is the case.
	» This also prevents issues with releasing an object down to retain count 0, then trying to retain it.
• Added releases before nil-ing or setting the property's ivar.
• Added retains in the assignment of the new object to the property's ivar.