Previous interfaces for these libcurl internal functions did not allow to tell
apart a legitimate zero size result from an error condition. These functions
now return a CURLcode indicating function success or otherwise specific error.
Output size is returned using a pointer argument.

All usage of these two functions, and others closely related, has been adapted
to the new interfaces. Relative error and OOM handling adapted or added where
missing. Unit test 1302 also adapted.

Fix compiler warning: conversion may lose significant bits

Fix compiler warning: variable was set but never used

Fix compiler warning: clobber ignored

Fix compiler warning: variable was set but never used

Fix compiler warning: clobber ignored

fix compiler warning

convert Curl_ultous() and Curl_ultouc() functions to curlx_ultous() and
curlx_ultouc(), exposing them through curlx.h to allow proper code reuse
later in our test harness.

fix compiler warning

fix compiler warning

removed trailing whitespace

in a slightly better way for more platforms. The $HOME is only used for
.curlrc atm, but the possible upcoming change of .netrc treatment may also
need the home dir.