Bug#797858: devscripts: build-rdeps

[Osamu Aoki]

Hi,

This new code is slow (100x-150x) but does a good job finding
dependencies which old code was useless.  Here is the record:

$ time build-rdeps libopencc-dev
Reverse Build-depends in contrib:
---------------------------------

No reverse build-depends found for libopencc-dev.

Reverse Build-depends in main:
------------------------------

ibus-libzhuyin
ibus-pinyin
libpyzy
librime

Found a total of 4 reverse build-depend(s) for libopencc-dev.

Reverse Build-depends in non-free:
----------------------------------

No reverse build-depends found for libopencc-dev.


real	0m15.360s
user	0m15.156s
sys	0m0.200s


$ time build-rdeps --old libopencc-dev
Reverse Build-depends in contrib:
---------------------------------

No reverse build-depends found for libopencc-dev.

Reverse Build-depends in main:
------------------------------

librime
libpyzy
ibus-pinyin
ibus-libzhuyin

Found a total of 4 reverse build-depend(s) for libopencc-dev.

Reverse Build-depends in non-free:
----------------------------------

No reverse build-depends found for libopencc-dev.


real	0m0.241s
user	0m0.220s
sys	0m0.012s

====================================================================================
$ time build-rdeps libopencc1
Reverse Build-depends in contrib:
---------------------------------

No reverse build-depends found for libopencc1.

Reverse Build-depends in main:
------------------------------

brise
fcitx-rime
ibus-libzhuyin
ibus-pinyin
ibus-rime
libpyzy
librime

Found a total of 7 reverse build-depend(s) for libopencc1.

Reverse Build-depends in non-free:
----------------------------------

No reverse build-depends found for libopencc1.


real	0m15.297s
user	0m15.068s
sys	0m0.220s

$ time build-rdeps --old libopencc1
Reverse Build-depends in contrib:
---------------------------------

No reverse build-depends found for libopencc1.

Reverse Build-depends in main:
------------------------------

No reverse build-depends found for libopencc1.

Reverse Build-depends in non-free:
----------------------------------

No reverse build-depends found for libopencc1.


real	0m0.227s
user	0m0.212s
sys	0m0.004s

Osamu