Add support for iterating over all vertices in {dfs,bfs,dijkstra}_{search,iterator}()

6 jobs for master in 184 minutes and 22 seconds (queued for 1 second)
Status Job ID Name Coverage
  Test
passed #2243
amd64
job_clang_amd64

03:04:20

passed #2247
amd64
job_clang_amd64_nosh

03:02:49

passed #2245
amd64
job_clang_py2_amd64

03:04:21

passed #2242
amd64
job_gcc_amd64

02:18:15

passed #2246
amd64
job_gcc_amd64_nosh

02:17:00

passed #2244
amd64
job_gcc_py2_amd64

02:19:48