add process snapshots as a file type.  also, correct bug in identifying
pem certificates.  unfortunately, ghostscript has a leading null, so
the length field can't be eliminated.

Reference: /n/sources/patch/applied/filesnapfs
Date: Tue Dec 18 19:55:47 CET 2007
Signed-off-by: quanstro@quanstro.net

--- /sys/src/cmd/file.c	Tue Dec 18 19:54:29 2007
+++ /sys/src/cmd/file.c	Tue Dec 18 19:54:20 2007
@@ -803,23 +803,27 @@
 	".tr",			"troff input",		3,	"text/troff",
 	"vac:",			"venti score",		4,	"text/plain",
 	"-----BEGIN CERTIFICATE-----\n",
-				"pem certificate",	3,	"text/plain",
+				"pem certificate",	-1,	"text/plain",
 	"-----BEGIN TRUSTED CERTIFICATE-----\n",
-				"pem trusted certificate", 3,	"text/plain",
+				"pem trusted certificate", -1,	"text/plain",
 	"-----BEGIN X509 CERTIFICATE-----\n",
-				"pem x.509 certificate", 3,	"text/plain",
-	"subject=/C=",		"pem certificate with header", 3, "text/plain",
+				"pem x.509 certificate", -1,	"text/plain",
+	"subject=/C=",		"pem certificate with header", -1, "text/plain",
+	"process snapshot ",	"process snapshot",	-1,	"application/snapfs",
 	0,0,0,0
 };
 
 int
 istring(void)
 {
-	int i;
+	int i, l;
 	struct FILE_STRING *p;
 
 	for(p = file_string; p->key; p++) {
-		if(nbuf >= p->length && !memcmp(buf, p->key, p->length)) {
+		l = p->length;
+		if(l == -1)
+			l = strlen(p->key);
+		if(nbuf >= l && !memcmp(buf, p->key, l)) {
 			if(mime)
 				print("%s\n", p->mime);
 			else