- Fix mysqld_safe so that it always passes correct --log-error argument to mysqld
- A few other minor clean-ups to mysqld_safe


scripts/mysqld_safe.sh:
  Bug #6061 mysql-log-rotate script - error logging doesn't use new file
  
  - Change mysqld_safe to pass --log-error to mysqld in all cases.  The old behavior was to usually "swallow" the --log-error=file.name argument, which caused mysqld to write to stderr and not be able to flush the error log file.  Ironically, passing --log-error (with no file name) seemed to work fine, because mysqld_safe didn't recognize it and passed it on to mysqld as an unknown option.
  - Ensure that the error log file matches what mysqld uses; in particular, add ".err" if given a --log-error argument with no extension, and add "$DATADIR" to the front of a relative path
  - Various other mysqld_safe clean-ups while there - quote arguments properly, remove some redundant code