Extend buffer for reading lines from /proc.

Apparently a line longer than 255 chars was spotted in the wild:
http://serverfault.com/questions/577939/linux-ps-htop-show-processes-running-for-hundreds-or-thousands-of-days-though-h#comment676098_577939

linux/LinuxProcessList.h

@@ -59,6 +59,10 @@ typedef struct LinuxProcessList_ {
 #define PROCMEMINFOFILE PROCDIR "/meminfo"
 #endif
 
+#ifndef PROC_LINE_LENGTH
+#define PROC_LINE_LENGTH 512
+#endif
+
    
 ProcessList* ProcessList_new(UsersTable* usersTable, Hashtable* pidWhiteList, uid_t userId);