ardour: 4.1 -> 4.2 (fix the git revision and hash to _really_ pull the latest 4.2)

[fps]

The default ardour package claimed to be based off version 4.2 but pulled a git rev which corresponded to 4.1. This PR just fixes the git rev and hash.

The nix exp also has some probably unnecessary cruft in it which I'll take a look at when 4.3 comes out.

Compiled and runs locally on channel 15.09

[fps]

  CC       vmpool.lo
libtool: link: ( cd ".libs" && rm -f "im-cedilla.la" && ln -s "../im-cedilla.la" "im-cedilla.la" )
libtool: link: ( cd ".libs" && rm -f "im-ipa.la" && ln -s "../im-ipa.la" "im-ipa.la" )
libtool: link: ( cd ".libs" && rm -f "im-am-et.la" && ln -s "../im-am-et.la" "im-am-et.la" )
libtool: link: ( cd ".libs" && rm -f "im-viqr.la" && ln -s "../im-viqr.la" "im-viqr.la" )
libtool: link: ( cd ".libs" && rm -f "im-multipress.la" && ln -s "../im-multipress.la" "im-multipress.la" )
libtool: link: ( cd ".libs" && rm -f "im-ti-er.la" && ln -s "../im-ti-er.la" "im-ti-er.la" )
  CC       vmprivate.lo
libtool: link: ( cd ".libs" && rm -f "im-inuktitut.la" && ln -s "../im-inuktitut.la" "im-inuktitut.la" )
libtool: link: ( cd ".libs" && rm -f "im-ti-et.la" && ln -s "../im-ti-et.la" "im-ti-et.la" )
libtool: link: ( cd ".libs" && rm -f "im-cyrillic-translit.la" && ln -s "../im-cyrillic-translit.la" "im-cyrillic-translit.la" )
vmprivate.c: In function 'vmextend':
vmprivate.c:174:2: warning: dereferencing type-punned pointer will break strict-aliasing rules [-Wstrict-aliasing]
  CLRPFREE(SIZE(NEXT(t)));
  ^
The log length has exceeded the limit of 4 Megabytes (this usually means that test suite is raising the same exception over and over).
The build has been terminated.

[cillianderoiste]

Excellent, thanks!

[fps]

you're very welcome :)