Print build XML in pretty print format per default

The build XML file is written as a compact file currently. This was meant to safe processing time. But the readability of the file should be the major concern since users who do not want this report may skip its generation anyway.

Therefore: The default should be changed.

The API is broken for those that depend on the compressed output. A XML parser does not mind, therefore we deem this break of API not problematical.