pt_BR.ISO8859-1/books/handbook: New pt_BR translation into .po format

• content synchronized with en_US document (r52873)
• book.xml converted to .po
• .po file was translated to pt_BR
• .po and .xml file has been set to UTF-8 encoding
• information about volunteers who translated and/or revised the document was added to the header of the .po file.

Obtained from: The FreeBSD Brazilian Portuguese Documentation Project