Make false/true into builtins

Making `true` into a builtin is a significant optimization to `while
true` loops. As long as `true` is a builtin, we may as well make `false`
builtin as well (despite the fact that it's not typically executed in a
loop).

builtin.cpp

@@ -4001,6 +4001,16 @@ int builtin_parse(parser_t &parser, wchar_t **argv)
     return STATUS_BUILTIN_OK;
 }
 
+int builtin_true(parser_t &parser, wchar_t **argv)
+{
+    return STATUS_BUILTIN_OK;
+}
+
+int builtin_false(parser_t &parser, wchar_t **argv)
+{
+    return STATUS_BUILTIN_ERROR;
+}
+
 /*
   END OF BUILTIN COMMANDS
   Below are functions for handling the builtin commands.
@@ -4038,6 +4048,7 @@ static const builtin_data_t builtin_datas[]=
     { 		L"end",  &builtin_generic, N_(L"End a block of commands")   },
     { 		L"exec",  &builtin_generic, N_(L"Run command in current process")  },
     { 		L"exit",  &builtin_exit, N_(L"Exit the shell") },
+    { 		L"false",  &builtin_false, N_(L"Return an unsuccessful result") },
     { 		L"fg",  &builtin_fg, N_(L"Send job to foreground")   },
     { 		L"for",  &builtin_generic, N_(L"Perform a set of commands multiple times")   },
     { 		L"function",  &builtin_generic, N_(L"Define a new function")   },
@@ -4058,6 +4069,7 @@ static const builtin_data_t builtin_datas[]=
     { 		L"status",  &builtin_status, N_(L"Return status information about fish")  },
     { 		L"switch",  &builtin_generic, N_(L"Conditionally execute a block of commands")   },
     { 		L"test",  &builtin_test, N_(L"Test a condition")   },
+    { 		L"true",  &builtin_true, N_(L"Return a successful result") },
     { 		L"ulimit",  &builtin_ulimit, N_(L"Set or get the shells resource usage limits")  },
     { 		L"while",  &builtin_generic, N_(L"Perform a command multiple times")   }
 };

doc_src/false.txt

@@ -0,0 +1,10 @@
+\section false false - return an unsuccessful result
+
+\subsection false-synopsis Synopsis
+\fish{synopsis}
+false
+\endfish
+
+\subsection false-description Description
+
+`false` sets the exit status to 1.

doc_src/true.txt

@@ -0,0 +1,10 @@
+\section true true - return a successful result
+
+\subsection true-synopsis Synopsis
+\fish{synopsis}
+true
+\endfish
+
+\subsection true-description Description
+
+`true` sets the exit status to 0.

fish.xcodeproj/project.pbxproj

@@ -926,6 +926,8 @@
 				"$(SRCROOT)/doc_src/umask.txt",
 				"$(SRCROOT)/doc_src/vared.txt",
 				"$(SRCROOT)/doc_src/while.txt",
+				"$(SRCROOT)/doc_src/true.txt",
+				"$(SRCROOT)/doc_src/false.txt",
 			);
 			outputPaths = (
 				"$(BUILT_PRODUCTS_DIR)/man/man1/alias.1",
@@ -998,6 +1000,8 @@
 				"$(BUILT_PRODUCTS_DIR)/man/man1/umask.1",
 				"$(BUILT_PRODUCTS_DIR)/man/man1/vared.1",
 				"$(BUILT_PRODUCTS_DIR)/man/man1/while.1",
+				"$(BUILT_PRODUCTS_DIR)/man/man1/true.1",
+				"$(BUILT_PRODUCTS_DIR)/man/man1/false.1",
 			);
 			runOnlyForDeploymentPostprocessing = 0;
 			shellPath = /bin/sh;