[gdb/contrib] Add "doens't->doesn't" to common-misspellings.txt

Add "doens't->doesn't" to gdb/contrib/common-misspellings.txt, and run
gdb/contrib/spellcheck.sh to fix this in a few files.

Tested on x86_64-linux.

Approved-by: Kevin Buettner <kevinb@redhat.com>

gdb/contrib/common-misspellings.txt

@@ -16,3 +16,4 @@
 
 inbetween->between, in between, in-between
 sofar->so far
+doens't->doesn't

gdb/testsuite/gdb.ada/str_chars.exp

@@ -57,7 +57,7 @@ gdb_test "print Arg" \
 
 # The 'set print elements' command used to control printing of characters
 # in a string, before we created 'set print characters'.  This test makes
-# sure that 'set print elements' doens't effect string printing any more.
+# sure that 'set print elements' doesn't effect string printing any more.
 gdb_test_no_output "set print elements 12"
 gdb_test "print Arg" \
     " = \"abcdefghijklmnopqrstuvwxyz\"" \

gdb/testsuite/gdb.dwarf2/dw2-bad-elf.exp

@@ -123,7 +123,7 @@ Dwarf::assemble $asm_file {
 	include_dir "${srcdir}/${subdir}"
 	file_name "$srcfile" 1
 
-	# Line data doens't need to be correct, just present.
+	# Line data doesn't need to be correct, just present.
 	program {
 	    DW_LNE_set_address [lindex $main_result 0]
 	    DW_LNS_advance_line 10
@@ -142,7 +142,7 @@ Dwarf::assemble $asm_file {
 	include_dir "${srcdir}/${subdir}"
 	file_name "dw2-bad-elf-other.c" 1
 
-	# Line data doens't need to be correct, just present.
+	# Line data doesn't need to be correct, just present.
 	program {
 	    DW_LNE_set_address some_func
 	    DW_LNS_advance_line 5

gdb/testsuite/lib/tuiterm.exp

@@ -1178,7 +1178,7 @@ namespace eval Term {
     }
 
     # Check the contents of a box on the screen.  This is a little
-    # like check_contents, but doens't check the whole screen
+    # like check_contents, but doesn't check the whole screen
     # contents, only the contents of a single box.  This procedure
     # includes (effectively) a call to check_box to ensure there is a
     # box where expected, if there is then the contents of the box are