add test for diffing identical binary files

tests/test-diff-binary-file

@@ -0,0 +1,25 b''
+#!/bin/sh
+
+hg init a
+cd a
+cp $TESTDIR/binfile.bin .
+hg add binfile.bin
+hg ci -m 'add binfile.bin' -d '0 0'
+
+echo >> binfile.bin
+hg ci -m 'change binfile.bin' -d '0 0'
+
+hg revert -r 0 binfile.bin
+hg ci -m 'revert binfile.bin' -d '0 0'
+
+echo % diff -r 0 -r 1
+hg diff --nodates -r 0 -r 1
+
+echo % diff -r 0 -r 2
+hg diff --nodates -r 0 -r 2
+
+echo % diff --git -r 0 -r 1
+hg diff --git -r 0 -r 1
+
+echo % diff --git -r 0 -r 2
+hg diff --git -r 0 -r 2

tests/test-diff-binary-file.out

@@ -0,0 +1,24 b''
+% diff -r 0 -r 1
+diff -r 48b371597640 -r acea2ab458c8 binfile.bin
+Binary file binfile.bin has changed
+% diff -r 0 -r 2
+% diff --git -r 0 -r 1
+diff --git a/binfile.bin b/binfile.bin
+index 37ba3d1c6f17137d9c5f5776fa040caf5fe73ff9..58dc31a9e2f40f74ff3b45903f7d620b8e5b7356
+GIT binary patch
+literal 594
+zc$@)J0<HatP)<h;3K|Lk000e1NJLTq000mG000mO0ssI2kdbIM00009a7bBm000XU
+z000XU0RWnu7ytkO2XskIMF-Uh9TW;VpMjwv0005-Nkl<ZD9@FWPs=e;7{<>W$NUkd
+zX$nnYLt$-$V!?uy+1V%`z&Eh=ah|duER<4|QWhju3gb^nF*8iYobxWG-qqXl=2~5M
+z*IoDB)sG^CfNuoBmqLTVU^<;@nwHP!1wrWd`{(mHo6VNXWtyh{alzqmsH*yYzpvLT
+zLdY<T=ks|woh-`&01!ej#(xbV1f|pI*=%;d-%F*E*X#ZH`4I%6SS+$EJDE&ct=8po
+ziN#{?_j|kD%Cd|oiqds`xm@;oJ-^?NG3Gdqrs?5u*zI;{nogxsx~^|Fn^Y?Gdc6<;
+zfMJ+iF1J`LMx&A2?dEwNW8ClebzPTbIh{@$hS6*`kH@1d%Lo7fA#}N1)oN7`gm$~V
+z+wDx#)OFqMcE{s!JN0-xhG8ItAjVkJwEcb`3WWlJfU2r?;Pd%dmR+q@mSri5q9_W-
+zaR2~ECX?B2w+zELozC0s*6Z~|QG^f{3I#<`?)Q7U-JZ|q5W;9Q8i_=pBuSzunx=U;
+z9C)5jBoYw9^?EHyQl(M}1OlQcCX>lXB*ODN003Z&P17_@)3Pi=i0wb04<W?v-u}7K
+zXmmQA+wDgE!qR9o8jr`%=ab_&uh(l?R=r;Tjiqon91I2-hIu?57~@*4h7h9uORK#=
+gQItJW-{SoTm)8|5##k|m00000NkvXXu0mjf3JwksH2?qr
+
+% diff --git -r 0 -r 2
+diff --git a/binfile.bin b/binfile.bin