... to make it hold microseconds too.

Fixes #4165
Closes #4168

... by using curl_off_t for the typedef if time_t is larger than 4
bytes.

Reported-by: Gisle Vanem
Bug: https://github.com/curl/curl/commit/b9d25f9a6b3ca791385b80a6a3c3fa5ae113e1e0#co
mmitcomment-25205058
Closes #2019

... since the 'tv' stood for timeval and this function does not return a
timeval struct anymore.

Also, cleaned up the Curl_timediff*() functions to avoid typecasts and
clean up the descriptive comments.

Closes #2011

... to cater for systems with unsigned time_t variables.

- Renamed the functions to curlx_timediff and Curl_timediff_us.

- Added overflow protection for both of them in either direction for
  both 32 bit and 64 bit time_ts

- Reprefixed the curlx_time functions to use Curl_*

Reported-by: Peter Piekarski
Fixes #2004
Closes #2005

... to make all libcurl internals able to use the same data types for
the struct members. The timeval struct differs subtly on several
platforms so it makes it cumbersome to use everywhere.

Ref: #1652
Closes #1693

This gives us accurate precision and it allows us to avoid storing "no
time" for systems with too low timer resolution as we then bump the time
up to 1 microsecond. Should fix test 573 on windows.

Remove the now unused curlx_tvdiff_secs() function.

Maintains the external getinfo() API with using doubles.

Fixes #1531

Fix bugs and compiler warnings on systems with 32-bit long and
64-bit time_t.

Reviewed-by: Daniel Stenberg

Closes #1499

... as long is still 32bit on modern 64bit windows machines, while
time_t is generally 64bit.