This patch adds missing newlines, trims multiple redundant final
newlines into a single one, and trims redundant leading newlines.

According to POSIX, a line is a sequence of zero or more non-' <newline>'
characters plus a terminating '<newline>' character. [1] Files should
normally have at least one final newline character.

C89 [2] and later standards [3] mention a final newline:
"A source file that is not empty shall end in a new-line character,
which shall not be immediately preceded by a backslash character."

Although it is not mandatory for all files to have a final newline
fixed, a more consistent and homogeneous approach brings less of commit
differences issues and a better development experience in certain text
editors and IDEs.

[1] http://pubs.opengroup.org/onlinepubs/9699919799/basedefs/V1_chap03.html#tag_03_206
[2] https://port70.net/~nsz/c/c89/c89-draft.html#2.1.1.2
[3] https://port70.net/~nsz/c/c99/n1256.html#5.1.1.2

* PHP-7.1:
  Fix #75944: Wrong cp1251 detection

`\xFF` is a valid character of CP-1251.

* PHP-7.1:
  Fix #62545: wrong unicode mapping in some charsets

Undefined characters are best mapped to Unicode REPLACEMENT characters.

The introduced checks were not correct in two respects:
 * It was checked whether the source encoding of the string matches
   the internal encoding, while the actually relevant encoding is
   the *target* encoding.
 * Even if the correct encoding is used, the checks are still too
   conservative. Just because something is not a "Unicode-encoding"
   does not mean that it does not map any non-ASCII characters.

I've reverted the added checks and instead adjusted mbfl_convert
to first try to use the provided substitution character and if
that fails, perform the fallback to '?' at that point. This means
that any codepoint mapped in the target encoding should now be
correctly supported and anything else should fall back to '?'.