Add convenience attribute operator to NodeSeq

[rtyley]

Compared to the current method of reading the string text of an attribute:

(x \ "@bar").text

...the new operator removes the need for a pair of parenthesis and shortens the overall expression by 7 chars :

x \@ "bar"

Discussion on scala-internals:

https://groups.google.com/d/topic/scala-internals/BZ-tfbebDqE/discussion

Review by @phaller

[scala-jenkins]

Started jenkins job pr-scala-testsuite-linux-opt at https://scala-webapps.epfl.ch/jenkins/job/pr-scala-testsuite-linux-opt/1743/

[scala-jenkins]

jenkins job pr-scala-testsuite-linux-opt: Success - https://scala-webapps.epfl.ch/jenkins/job/pr-scala-testsuite-linux-opt/1743/

[scala-jenkins]

Started jenkins job pr-rangepos at https://scala-webapps.epfl.ch/jenkins/job/pr-rangepos/1032/

[scala-jenkins]

jenkins job pr-rangepos: Success - https://scala-webapps.epfl.ch/jenkins/job/pr-rangepos/1032/

[soc]

What about \\@?

[rtyley]

@soc interesting question - \\@ would mean 'give me the (concatenated or traversable?) values of every attribute with this name under the current nodeseq' - although it could be a useful shortcut, I typically wouldn't read the value of an attribute without first knowing the name of the element it belonged to.

For me, this means that although I feel comfortable with \@, I would rather not have \\@ included.

[rtyley]

btw, I have mailed a signed copy of the Scala CLA to Danielle Chamberlain.

[adriaanm]

ping @phaller

[phaller]

LGTM