Concatenate JavaScripts with semicolon.

[lynaghk]

Without a semicolon, JavaScript evaluates

a = b + c
(d + e).print()

as

a = b + c(d + e).print();

rather than

a = b + c;
(d + e).print();

This commit prevents that from happening by defensively adding a semicolon when joining JavaScripts.

[dnsco]

is this going to get merged? we occasionally have issues resulting from concatenation.

[dougcole]

This seems really valuable - is anything holding this up?

[andrewhao]

What compressors are you all using? By explicitly requiring Closure Compiler this issue went away for me (methinks JSMin uses a naive compression algorithm?).