hghave: cache the result of gethgversion
hghave --test-features calls it 90 times, each one calling hg --version
which takes a tenth of a second on my workstation, adding up to about
10s win on test-hghave.t.
Fixes https://bugs.debian.org/939756
Differential Revision: https://phab.mercurial-scm.org/D8092
{
// Enforcing
"eqeqeq" : true, // true: Require triple equals (===) for comparison
"forin" : true, // true: Require filtering for..in loops with obj.hasOwnProperty()
"freeze" : true, // true: prohibits overwriting prototypes of native objects such as Array, Date etc.
"nonbsp" : true, // true: Prohibit "non-breaking whitespace" characters.
"undef" : true, // true: Require all non-global variables to be declared (prevents global leaks)
// Environments
"browser" : true // Web Browser (window, document, etc)
}