libc: rewrite putenv and getenv.

These new implementations

- do several validity check on input parameters
- allow a bit larger variable names (127 bytes, aka sizeof(Proc.genbuf)-1)
- preserve nulls in the content (the original version used to replace
  '\0' with ' '). I can't see why they did, actually.
  See also http://marc.info/?l=9fans&m=148475801229908&w=2

Should also fix CID 155718

qa/lib/c/build.json

@@ -8,6 +8,9 @@
 			"-std=gnu11"
 		],
 		"Install": "/arch/$ARCH/qa/lib/c",
+		"Post": [
+			"cp *.rc $JEHANNE/arch/$ARCH/qa/lib/c/"
+		],
 		"SourceFilesCmd": [
 			"asmscall.c",
 			"cleanname.c",

qa/lib/c/env.rc

@@ -0,0 +1,28 @@
+#!/cmd/rc
+
+# verify that environment variables can have names 127 byte long
+# why 127? because it's the size of genbuf in the kernel's Proc structure
+# minus the ending \0
+
+abcdef0123456789abcdef0123456789abcdef0123456789abcdef0123456789abcdef0123456789abcdef0123456789abcdef0123456789abcdef012345678=10
+if ( ! ~ $abcdef0123456789abcdef0123456789abcdef0123456789abcdef0123456789abcdef0123456789abcdef0123456789abcdef0123456789abcdef012345678 10 ) {
+	echo FAIL: cannot read an environment variable with a long name
+	exit FAIL
+}
+
+# verify that rc lists work
+list=(How now brown cow)
+string=$"list
+
+if( ! ~ $#list 4 ) {
+	echo FAIL: list count does not work on a 4 elements list
+	exit FAIL
+}
+
+if( ! ~ $#string 1 ) {
+	echo FAIL: list count does not work on a single string
+	exit FAIL
+}
+
+echo PASS
+exit PASS