genrule() should fail if any command fails.

Summary:
From #16.

If a genrule is a complex sequence of shell commands the rule
should fail if any of the commands fails and its exit status was
not examined.

Fixes #21

Test Plan: Sandcastle builds.

src/com/facebook/buck/shell/AbstractGenruleStep.java

@@ -103,7 +103,7 @@ public String getShortName() {
   protected ImmutableList<String> getShellCommandInternal(ExecutionContext context) {
     // The priority sequence is
     //   "cmd.exe /c winCommand" (Windows Only)
-    //   "/bin/bash -c shCommand" (Non-windows Only)
+    //   "/bin/bash -e -c shCommand" (Non-windows Only)
     //   "(/bin/bash -c) or (cmd.exe /c) cmd" (All platforms)
     String command;
     if (context.getPlatform() == Platform.WINDOWS) {
@@ -129,7 +129,7 @@ protected ImmutableList<String> getShellCommandInternal(ExecutionContext context
             getFullyQualifiedName());
       }
       command = replaceMatches(context.getProjectFilesystem(), commandInUse);
-      return ImmutableList.of("/bin/bash", "-c", command);
+      return ImmutableList.of("/bin/bash", "-e", "-c", command);
     }
   }
 

test/com/facebook/buck/android/ApkGenruleTest.java

@@ -223,7 +223,7 @@ public void testCreateAndRunApkGenrule() throws IOException, NoSuchBuildTargetEx
         .put("OUT", expectedApkOutput).build(),
         genruleCommand.getEnvironmentVariables(executionContext));
     assertEquals(
-        ImmutableList.of("/bin/bash", "-c", "python signer.py $APK key.properties > $OUT"),
+        ImmutableList.of("/bin/bash", "-e", "-c", "python signer.py $APK key.properties > $OUT"),
         genruleCommand.getShellCommand(executionContext));
 
     EasyMock.verify(parser);

test/com/facebook/buck/shell/GenruleTest.java

@@ -233,7 +233,7 @@ public void testCreateAndRunGenrule() throws IOException, NoSuchBuildTargetExcep
         .build(),
         genruleCommand.getEnvironmentVariables(executionContext));
     assertEquals(
-        ImmutableList.of("/bin/bash", "-c", "python convert_to_katana.py AndroidManifest.xml > $OUT"),
+        ImmutableList.of("/bin/bash", "-e", "-c", "python convert_to_katana.py AndroidManifest.xml > $OUT"),
         genruleCommand.getShellCommand(executionContext));
   }
 
@@ -511,7 +511,7 @@ public void testGetShellCommand() {
         .build(new BuildRuleResolver());
 
     ImmutableList<String> command = rule.createGenruleStep().getShellCommand(linuxExecutionContext);
-    assertEquals(ImmutableList.of("/bin/bash", "-c", bash), command);
+    assertEquals(ImmutableList.of("/bin/bash", "-e", "-c", bash), command);
 
     command = rule.createGenruleStep().getShellCommand(windowsExecutionContext);
     assertEquals(ImmutableList.of("cmd.exe", "/c", cmdExe), command);
@@ -523,7 +523,7 @@ public void testGetShellCommand() {
         .setOut("out.txt")
         .build(new BuildRuleResolver());
     command = rule.createGenruleStep().getShellCommand(linuxExecutionContext);
-    assertEquals(ImmutableList.of("/bin/bash", "-c", cmd), command);
+    assertEquals(ImmutableList.of("/bin/bash", "-e", "-c", cmd), command);
 
     command = rule.createGenruleStep().getShellCommand(windowsExecutionContext);
     assertEquals(ImmutableList.of("cmd.exe", "/c", cmd), command);