revlog: add optional stoprev arg to revlog.ancestors()
This will be used as a step in removing reachable() in a future diff.
Doing it now because bryano is in the process of rewriting ancestors in
C. This depends on bryano's patch to replace *revs with revs in the
declaration of revlog.ancestors.
A = 'data/aux.bla/bla.aux/prn/PRN/lpt/com3/nul/coma/foo.NUL/normal.c.i'
B = 'data/au~78.bla/bla.aux/pr~6e/_p_r_n/lpt/co~6d3/nu~6c/coma/foo._n_u_l/normal.c.i'
A = 'data/AUX/SECOND/X.PRN/FOURTH/FI:FTH/SIXTH/SEVENTH/EIGHTH/NINETH/TENTH/ELEVENTH/LOREMIPSUM.TXT.i'
B = 'dh/au~78/second/x.prn/fourth/fi~3afth/sixth/seventh/eighth/nineth/tenth/loremia20419e358ddff1bf8751e38288aff1d7c32ec05.i'
A = 'data/enterprise/openesbaddons/contrib-imola/corba-bc/netbeansplugin/wsdlExtension/src/main/java/META-INF/services/org.netbeans.modules.xml.wsdl.bindingsupport.spi.ExtensibilityElementTemplateProvider.i'
B = 'dh/enterpri/openesba/contrib-/corba-bc/netbeans/wsdlexte/src/main/java/org.net7018f27961fdf338a598a40c4683429e7ffb9743.i'
A = 'data/AUX.THE-QUICK-BROWN-FOX-JU:MPS-OVER-THE-LAZY-DOG-THE-QUICK-BROWN-FOX-JUMPS-OVER-THE-LAZY-DOG.TXT.i'
B = 'dh/au~78.the-quick-brown-fox-ju~3amps-over-the-lazy-dog-the-quick-brown-fox-jud4dcadd033000ab2b26eb66bae1906bcb15d4a70.i'
A = 'data/Project Planning/Resources/AnotherLongDirectoryName/Followedbyanother/AndAnother/AndThenAnExtremelyLongFileName.txt'
B = 'dh/project_/resource/anotherl/followed/andanoth/andthenanextremelylongfilenaf93030515d9849cfdca52937c2204d19f83913e5.txt'
A = 'data/Project.Planning/Resources/AnotherLongDirectoryName/Followedbyanother/AndAnother/AndThenAnExtremelyLongFileName.txt'
B = 'dh/project_/resource/anotherl/followed/andanoth/andthenanextremelylongfilena0fd7c506f5c9d58204444fc67e9499006bd2d445.txt'
A = 'data/foo.../foo / /a./_. /__/.x../ bla/.FOO/something.i'
B = 'data/foo..~2e/foo ~20/~20/a~2e/__.~20/____/~2ex.~2e/~20 bla/~2e_f_o_o/something.i'