change redisplay to handle some cases where the line consumes more than the number of physical screen lines; add regerror() error messages if regular expression compilation fails; make sure active region readline variables are displayed with bind -v; partial fix for bind -x and commands containing quoting characters

tests/cond-regexp2.sub

@@ -21,6 +21,16 @@
 
 [[ "\\" =~ [\\] ]] || echo bad 5
 
+[[ x =~ [z-a] ]] && echo bad 6
+
+[[ x =~ [[:invalid:]abc] ]] && echo bad 7
+
+exp='x\'
+[[ x =~ $exp ]] && echo bad 8
+
+exp='a(xb'
+[[ x =~ $exp ]] && echo bad 9
+
 [[ dog =~ [[=d=]].. ]] && echo ok 1
 [[ d.. =~ [[=d=]]\.\. ]] && echo ok 2
 [[ dog =~ ['[=d=]'].. ]] && echo ok 3	# dubious

tests/cond.right

@@ -76,7 +76,11 @@ match control-a 2
 match control-a 3
 match control-a 4
 match control-a 5
-./cond-regexp2.sub: line 18: [[: invalid regular expression `[\.'
+./cond-regexp2.sub: line 18: [[: invalid regular expression `[\.': brackets ([ ]) not balanced
+./cond-regexp2.sub: line 24: [[: invalid regular expression `[z-a]': invalid character range
+./cond-regexp2.sub: line 26: [[: invalid regular expression `[[:invalid:]abc]': invalid character class
+./cond-regexp2.sub: line 29: [[: invalid regular expression `x\': trailing backslash (\)
+./cond-regexp2.sub: line 32: [[: invalid regular expression `a(xb': parentheses not balanced
 ok 1
 ok 2
 ok 3