ape: make libplumb available under ape.

This adds the mkfiles and plumb.h to ape,
similar to how libdraw is made available.
This is used for ports such as netsurf.

sys/include/ape/plumb.h

@@ -0,0 +1,57 @@
+#ifndef _PLAN9_SOURCE
+  This header file is an extension to ANSI/POSIX
+#endif
+
+#ifndef	__PLUMB_H_
+#define	__PLUMB_H_
+#pragma src "/sys/src/ape/lib/plumb"
+#pragma lib "/$M/lib/ape/libplumb.a"
+
+/*
+ * Message format:
+ *	source application\n
+ *	destination port\n
+ *	working directory\n
+ *	type\n
+ *	attributes\n
+ *	nbytes\n
+ *	n bytes of data
+ */
+
+typedef struct Plumbattr Plumbattr;
+typedef struct Plumbmsg Plumbmsg;
+
+struct Plumbmsg
+{
+	char		*src;
+	char		*dst;
+	char		*wdir;
+	char		*type;
+	Plumbattr	*attr;
+	int		ndata;
+	char		*data;
+};
+
+struct Plumbattr
+{
+	char		*name;
+	char		*value;
+	Plumbattr	*next;
+};
+
+int			plumbsend(int, Plumbmsg*);
+int			plumbsendtext(int, char*, char*, char*, char*);
+Plumbmsg*	plumbrecv(int);
+char*		plumbpack(Plumbmsg*, int*);
+Plumbmsg*	plumbunpack(char*, int);
+Plumbmsg*	plumbunpackpartial(char*, int, int*);
+char*		plumbpackattr(Plumbattr*);
+Plumbattr*	plumbunpackattr(char*);
+Plumbattr*	plumbaddattr(Plumbattr*, Plumbattr*);
+Plumbattr*	plumbdelattr(Plumbattr*, char*);
+void			plumbfree(Plumbmsg*);
+char*		plumblookup(Plumbattr*, char*);
+int			plumbopen(char*, int);
+int			eplumb(int, char*);
+
+#endif

sys/src/ape/lib/9/libc.h

@@ -159,6 +159,7 @@ extern	vlong	_NSEC(void);
 #define ERRMAX 128
 
 int errstr(char*, unsigned int);
+void rerrstr(char*, unsigned int);
 extern void sysfatal(char*, ...);
 
 extern	void		setmalloctag(void*, uintptr_t);

sys/src/ape/lib/9/mkfile

@@ -8,6 +8,7 @@ OFILES=\
 	crypt.$O\
 	ctime.$O\
 	errstr.$O\
+	rerrstr.$O\
 	getcallerpc.$O\
 	getfcr.$O\
 	getfields.$O\