flush an objects cache when mixin in

... if this object already is an mixin. Otherwise when mixin in
several things in a row, it would collect precomputed NFAs and
this would result in bigger files when serializing it.
Example: declare 10 infixes, was 9MB .pir file, is now 1.2MB.
         compiling it to pbc took 49s now takes 0.8s.
have an empty method decl
typo
Merge pull request #172 from cognominal/typo

typo
Generate local_lifetime hints.
s/local_lifetime/locallifetime/g
Nicer Attribute.gist
List asm-tree as a 3rdparty jar
Small optimisation in creating pairs

No reason to copy things if we can alias them.
Some error message corrections
Leave note for other people trying to use Inf/NaN as constants
Simplify .elems, we have $Inf!
JVM does not need ICU for any tests
Make []:(kv|p|k|v) work according to spec
correctly print $stop in s///-panic

This is a workaround for nqp issue #105.