Ensures that -K/--config inserts new items at the end of the list
instead of overwriting the second item, and that after a -K/--config
option has been parsed, the option parser's view of the current config
is update.

Fixes #5120
Closes #5123

Reported-by: bxac on github
Fixes #4730
Closes #4731

When looping, first trying '.curlrc' and then '_curlrc', the function
would not free the first string.

Closes #4731

Fall-back to _curlrc if the dot-version is missing.

Co-Authored-By: Steve Holme

Closes #4230

This is done by making sure each individual transfer is first added to a
linked list as then they can be performed serially, or at will, in
parallel.

Closes #3804

GetModuleFileName() returns a DWORD which is a typedef of an unsigned
long and not an int.

Closes #3980

Follow-up to 8144ba38.

Detected by Coverity CID 1445663
Closes #3976

Using the memdebug.h mem-leak feature, I noticed 2 calls like:
  FILE tool_parsecfg.c:70 fopen("c:\Users\Gisle\AppData\Roaming\_curlrc","rt")
  FILE tool_parsecfg.c:114 fopen("c:\Users\Gisle\AppData\Roaming\_curlrc","rt") 

No need for 'fopen(), 'fclose()' and a 'fopen()' yet again.

The function does not return the same value as snprintf() normally does,
so readers may be mislead into thinking the code works differently than
it actually does. A different function name makes this easier to detect.

Reported-by: Tomas Hoger
Assisted-by: Daniel Gustafsson
Fixes #3296
Closes #3297

- replace tabs with spaces where possible
- remove line ending spaces
- remove double/triple newlines at EOF
- fix a non-UTF-8 character
- cleanup a few indentations/line continuations
  in manual examples

Closes https://github.com/curl/curl/pull/3037