Make a copy of incoming options

[hershmire]

Options need to be copied since some properties are later deleted from the referenced object in Uglifyify. If copying does not occur, and the opts object is coming from an assigned variable, that object will be mutated with the deleted properties and any subsequent Uglifyify calls will not have the needed deleted properties – i.e. exts, x, global.

The test is modified to show this case.

[lrlna]

this is more or less similar to #69 and I kind of like this cleaner approach. What do you think about this @iamjochem ?

[iamjochem]

my thoughts:

1. the cloning of the options must occur in the write() function because otherwise two call to ujs.minify() can potentially interfere with each other's options (e.g. the sourcemap related options)

2. this PR is not deleting the properties on the options object that we know will cause uglyfy to choke ... we not only have to contend with uglyfy mutating the options object it is given but also with the possibility that we are being given an options object that contains properties that uglyfy will choke on.

3. it is bad practice (IMHO) to re-assign function parameters (last I read V8 refuses to fully optimize functions that reassign their parameters):

function foo(opts) { opts = extend(true, {}, opts); }

should be something like:

function foo(opts) { var _opts = extend(true, {}, opts); }

1. must be changed because otherwise it is still broken (but in an even more subtle way :-())
2. probably needs to change, although I'm not 100% sure this is the right place to do this.
3. not really important: it's some what of a an opinion, v8 best-practices for JS code is a moving target & we're generally talking about running short-lived cmd-line processes (quite likely that optimization for a function that is called just a couple of times does not even occur :-))

[iamjochem]

PS @lrlna - if you want me to rebase my PR so that it merges cleanly again please let me know

[hershmire]

Any update on fixing this?