...G...... [ZBXNEXT-1078] added 'proc.mem' 5-th parameter (memtype) on Solaris

Before this change:
   - psinfo.pr_size was the only process memory type supported.

This change:
   - adds 2 more process memory types: psinfo.pr_rssize and psinfo.pr_pctmem,
   - removes unnecessary call of zbx_stat(),
   - removes unnecessary converting of memory size from UI64 to 'double" and back to UI64,
   - renames 'memsize' variable to 'mem_size' for consistency with names of other variables.