convert x.toString() to ""+x instead of x+""

In some places this can save one byte in whitespace, e.g. after return.
Example:

function f(arg) {
        // return""+arg - no space between return and ""
        return arg.toString();
}
Merge pull request #41 from Skalman/toString-patch

Convert x.toString() to ""+x instead of x+""
fix invalid AST produced by dropping unused variable

close #44
v2.1.11
Add simple optimization for empty-string concats.

ref. #43
don't change order in binary expressions if both operands have side effects
Merge branch 'optimize_concat' of https://github.com/rvanvelzen/UglifyJS2 into rvanvelzen-optimize_concat
optimize constant switch blocks

ref. mishoo/UglifyJS#441
better solution for the last test in constant switch folding
Add support for somewhat preserving line numbers.

Usage: uglifyjs2 -b "beautify=0,preserve_line=1" /path/to/js

ref #46
retain (1,eval) as is when it's the expression of an AST_Call

otherwise we change the meaning of eval from global to lexical.
fix #51
rename the npm package to "uglify-js" and cli tool to "uglifyjs"
fix for https://github.com/mishoo/UglifyJS/issues/474
v2.2.1
fix #55
Fixed reading from STDIN.
Merge pull request #58 from roxeteer/master

Fixed reading from STDIN
Don't messup compressor stack while optimizing Switch

Fix #59
Add test for issue #59