allow for no overwrite option in convertLatLngs, #1092

[snkashis]

This provides for a parameter to allow people to bypass overwriting of existing arrays if needed.

References issue #1092

[tmcw]

This should always be on, rather than being an option: #1426

[danzel]

agreed, will tidy this up now.

[mourner]

@tmcw Agreed too. Was going to fix this for 0.6 and check all other places for such things.

[snkashis]

@mourner & @danzel, what else should I do here to get this ready? Just removed the option.

[mourner]

I'll check this out tomorrow, there may be some edge cases.

[danzel]

I've rebased a dev branch on your change and i'm working on it now, mainly writing some test cases to make sure everything is good.
I think the constructor and spliceLatLngs need some work too, but we'll see.

[danzel]

Looking good @snkashis.
Have pushed some tests up to a branch which includes your changes:
https://github.com/danzel/Leaflet/tree/convert_option