en: don't velarize n across word boundaries

It is possible -- especially at higher speeds -- for the n at the
end of a word to be velarised if the next word starts with a velar
plosive. I prefer the velarised sound between word boundaries, but
others do not. As such, limit the velarisation to within the word
only.

[1]	https://en.wikipedia.org/wiki/English_phonology

phsource/ph_english

 phoneme n
   vcd alv nas
   ipa n
-  IF nextPh(isVelar) THEN // /n/ is velarized to /N/ when before velar stops
+  IF nextPhW(isVelar) THEN // /n/ is velarized to /N/ when before velar stops
     ChangePhoneme(N)
   ENDIF
   CALL base1/n

tests/translate.test

 test_phonemes en " 'e@ri:zr'eInboU" "♈🌈"
 test_phonemes en " 'e@ri:z r'eInboU" "♈ 🌈"
 # multi-word
-test_phonemes en " Ekskla#m'eIS@N kw'EstS@n m'A@k" "⁉"
-test_phonemes en " Ekskla#m'eIS@N kw'EstS@n m'A@k r'eInboU" "⁉ 🌈"
+test_phonemes en " Ekskla#m'eIS@n kw'EstS@n m'A@k" "⁉"
+test_phonemes en " Ekskla#m'eIS@n kw'EstS@n m'A@k r'eInboU" "⁉ 🌈"
 
 # A list entry that uses '$text' to map to another list entry crashes 1.49.2 multi-word support:
 test_phonemes en " d'eIbju:t@d" "débuted"