avoid executing unsafe functions if we get a terminating signal while handling SIGCHLD; reject attempts to modify some attributes for readonly variables; more changes for unlocked stdio functions; quoting fixes for uncommon cases where IFS = ^A and the word is not being split

tests/array.right

@@ -70,7 +70,7 @@ declare -a d=([1]="test test")
 declare -a e=()
 declare -a f=([0]="" [1]="bdef" [2]="hello world" [3]="test" [4]="ninth element")
 ./array.tests: line 137: unset: ps1: not an array variable
-./array.tests: line 141: declare: c: cannot destroy array variables in this way
+./array.tests: line 141: declare: c: readonly variable
 this of
 this is a test of read using arrays
 this test