Prop210: Add attempt-based connection schedules
Existing tor schedules increment the schedule position on failure,
then retry the connection after the scheduled time.
To make multiple simultaneous connections, we need to increment the
schedule position when making each attempt, then retry a (potentially
simultaneous) connection after the scheduled time.
(Also change find_dl_schedule_and_len to find_dl_schedule, as it no
longer takes or returns len.)
Prop210: Add multiple simultaneous consensus downloads for clients
Make connections on TestingClientBootstrapConsensus*DownloadSchedule,
incrementing the schedule each time the client attempts to connect.
Check if the number of downloads is less than
TestingClientBootstrapConsensusMaxInProgressTries before trying any
more connections.
UseDefaultFallbackDirs enables any hard-coded fallback
directory mirrors. Default is 1, set it to 0 to disable fallbacks.
Implements ticket 17576.
Patch by "teor".
On FreeBSD backtrace(3) uses size_t instead of int (as glibc does). This
causes integer precision loss errors when we used int to store its
results.
The issue is fixed by using size_t to store the results of backtrace(3).
The manual page of glibc does not mention that backtrace(3) returns
negative values. Therefore, no unsigned integer wrapping occurs when its
result is stored in an unsigned data type.
Using variables removes the ambiguity about when to use variables and
when to use substitutions. Variables always work. Substitutions only
work when Autoconf knows about them which is not always the case.
The variables are also placed between quotes to ensures spaces in the
variables are handled properly.
Update the code for IPv6 authorities and fallbacks for function
argument changes.
Update unit tests affected by the function argument changes in
the patch.
Add unit tests for authority and fallback:
* adding via a function
* line parsing
* adding default authorities
(Adding default fallbacks is unit tested in #15775.)
