Use StringBuilder for String concatenations

[Jesper Öqvist]

ExtendJ 8.1.0-27-gcd7effa Java SE 5

ExtendJ implements string concatenation by using an implicit StringBuffer object. The StringBuilder class would be preferable since it behaves identically to StringBuffer except that its methods are not synchronized. There is no need to use thread-safe string buffers since each buffer object is only visible to a single thread.

Javac implements string concatenation by using StringBuilder.

[Jesper Öqvist]

String concatenation with StringBuilder

This changes code generation for string concatenation expressions (+, +=) to use StringBuilder instead of StringBuffer.

fixes #279 (bitbucket)

→ <<cset e6bd04c89dfe>>