Add getppid op (#422)

Allows a child process to get the parent process id, and thus
guess if it has become orphaned.

See: #381

Author: ugexe

docs/ops.markdown

@@ -296,6 +296,7 @@
   * [getenvhash](#getenvhash)
   * [backendconfig](#backendconfig)
   * [getpid](#getpid)
+  * [getppid `moar`](#getppid)
   * [jvmclasspaths `jvm`](#jvmclasspaths-jvm)
   * [sha1](#sha1)
   * [sleep](#sleep)
@@ -2491,6 +2492,11 @@ configure and build flags.
 
 Return the current process id, an int.
 
+## getppid `moar`
+* `getppid(--> int)`
+
+Return the process id of the parent process, an int.
+
 ## jvmclasspaths `jvm`
 * `jvmclasspaths(--> Mu)`
 

src/vm/moar/QAST/QASTOperationsMAST.nqp

@@ -2917,6 +2917,7 @@ QAST::MASTOperations.add_core_moarop_mapping('exit', 'exit', 0);
 QAST::MASTOperations.add_core_moarop_mapping('sleep', 'sleep', 0);
 QAST::MASTOperations.add_core_moarop_mapping('getenvhash', 'getenvhash');
 QAST::MASTOperations.add_core_moarop_mapping('getpid', 'getpid');
+QAST::MASTOperations.add_core_moarop_mapping('getppid', 'getppid');
 QAST::MASTOperations.add_core_moarop_mapping('gethostname', 'gethostname');
 QAST::MASTOperations.add_core_moarop_mapping('rand_i', 'rand_i');
 QAST::MASTOperations.add_core_moarop_mapping('rand_n', 'randscale_n');