reworked IOstreams

- Istream and Ostream now retain backslashes when reading/writing strings.
  The previous implementation simply discarded them, except when used to
  escape a double-quote or a newline. It is now vitally important to retain
  them, eg for quoting regular expression meta-characters.

  The backslash continues to be used as an escape character for double-quote
  and newline, but otherwise get passed through "as-is" without any other
  special meaning (ie, they are *NOT* C-style strings). This helps avoid
  'backslash hell'!
  For example,
     string:   "match real dots \.+, question mark \? or any char .*"
     C-style:  "match real dots \\.+, question mark \\? or any char .*"

- combined subfiles in db/IOstreams, some had more copyright info than code
- OPstreamI.H contained only private methods, moved into OPstream.C

Are these really correct?
   IOstreams/Istream.H:#   include "HashTable.C"
   token/token.H:#define NoHashTableC

src/OpenFOAM/primitives/strings/string/string.H

@@ -131,7 +131,7 @@ public:
             //- Count and return the number of a given character in the string
             size_type count(const char) const;
 
-            //- Is this string type valid
+            //- Is this string type valid?
             template<class String>
             static inline bool valid(const string&);