This updates the hunk header customization syntax.  The special
case 'funcname' attribute is gone.

You assign the name of the type of contents to path's "diff"
attribute as a string value in .gitattributes like this:

	*.java diff=java
	*.perl diff=perl
	*.doc diff=doc

If you supply "diff.<name>.funcname" variable via the
configuration mechanism (e.g. in $HOME/.gitconfig), the value is
used as the regexp set to find the line to use for the hunk
header (the variable is called "funcname" because such a line
typically is the one that has the name of the function in
programming language source text).

If there is no such configuration, built-in default is used, if
any.  Currently there are two default patterns: default and java.

Signed-off-by: Junio C Hamano <gitster@pobox.com>