Fix QTBUG-18934 by checking return value of qt_safe_pipe

When QProcess->start() is called, Qt creates a pipe to the process to
get its exit value and output.
It does this with qt_create_pipe, which calls qt_safe_pipe.
qt_safe_pipe, on failure, returns 1. qt_create_pipe then
sets errno and returns void.
The calling function, QProcessPrivate::startProcess, does not check
errno, and thus continues to fork the process, assuming the pipe has been
created successfully.

The child process then has no way to pass its exit value to the calling
process, since the communication pipes it would normally use do not
exist, and thus when it exits it becomes a zombie.

As a bonus, if waitForFinished is called on a broken process, a crash
results because it is trying to wait on a pipe which does not exist.

The fix makes qt_create_pipe return an integer, and QProcess::startProcess
check the return value, set processError and not create the child
process.

Task-Number: QTBUG-18934
Cherry-picked from qtbase f575dc214630b3e3ebd66477a623c78405724468
Change-Id: I2e1effdd0617be5b8c5492bcbcf5f2b1584b2241
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
Add support for SQLSTATE error codes

Postgres can report detailed information about an error using error codes.
See http://www.postgresql.org/docs/8.1/static/errcodes-appendix.html .
The current driver doesn't report the error, nor is it supported by the
QSqlError object.
The patch appends the error to the error message, helping applications to:
- handle different errors in a specific way
- show correct, translated error messages, independently on the language of the postgres installation

Change-Id: I5c7792606307afdefaeae37c512949c85c2c7674
Reviewed-by: Mark Brand <mabrand@mabrand.nl>
(cherry picked from commit qtbase/8ccab9b029ed2a2444d89a9cfc6c4a1866b8e82d)
Reviewed-by: Andy Shaw <andy.shaw@digia.com>