Description:
------------
Function imap_mime_header_decode() doesn't respect \t (HTAB) characters marking continuation of header defined in RFC822 as one of the LWSP chars, however SPACE is still ignored. Source string:

{{{
public 'subject' => string '=?utf-8?B?V3VzaHUgaW5mb3JtIC0gU2FjZW5zaWJhcyBJZ2F1bmk=?=	=?utf-8?B?amEgKFRhbGxpbmEpLCDRgdC+0YDQtdCy0L3QvtCy0LDQvdC40Y8g0LIg0KLQsNC7?=	=?utf-8?B?0LvQuNC90LUgMTEg0LTQtdC60LDQsdGA0Y8=?=' (length=182)
}}}

where spaces between =?...?= lines are actually tabs, results to
{{{
array
  0 => 
    object(stdClass)[54]
      public 'charset' => string 'utf-8' (length=5)
      public 'text' => string 'Wushu inform - Sacensibas Igauni' (length=32)
  1 => 
    object(stdClass)[53]
      public 'charset' => string 'default' (length=7)
      public 'text' => string '	' (length=1)
  2 => 
    object(stdClass)[55]
      public 'charset' => string 'utf-8' (length=5)
      public 'text' => string 'ja (Tallina), соревнования в Тал' (length=48)
  3 => 
    object(stdClass)[56]
      public 'charset' => string 'default' (length=7)
      public 'text' => string '	' (length=1)
  4 => 
    object(stdClass)[57]
      public 'charset' => string 'utf-8' (length=5)
      public 'text' => string 'лине 11 декабря' (length=26)

}}}

This produces:
{{{
Wushu inform - Sacensibas Igauni ja (Tallina), соревнования в Тал лине 11 декабря
}}}

with unwanted spaces in words "Igauni ja" and "Тал лине".

Test script:
---------------
    $str = "=?utf-8?B?V3VzaHUgaW5mb3JtIC0gU2FjZW5zaWJhcyBJZ2F1bmk=?="
        ."\t=?utf-8?B?amEgKFRhbGxpbmEpLCDRgdC+0YDQtdCy0L3QvtCy0LDQvdC40Y8g0LIg0KLQsNC7?="
        ."\t=?utf-8?B?0LvQuNC90LUgMTEg0LTQtdC60LDQsdGA0Y8=?=";

    var_dump(imap_mime_header_decode($str));
    var_dump(imap_mime_header_decode(str_replace("\t", " ", $str)))

Expected result:
----------------
array
  0 => 
    object(stdClass)[5]
      public 'charset' => string 'utf-8' (length=5)
      public 'text' => string 'Wushu inform - Sacensibas Igauni' (length=32)
  1 => 
    object(stdClass)[4]
      public 'charset' => string 'utf-8' (length=5)
      public 'text' => string 'ja (Tallina), б�аОб�аЕаВаНаОаВаАаНаИб� аВ аЂаАаЛ' (length=48)
  2 => 
    object(stdClass)[3]
      public 'charset' => string 'utf-8' (length=5)
      public 'text' => string 'аЛаИаНаЕ 11 аДаЕаКаАаБб�б�' (length=26)


Actual result:
--------------
array
  0 => 
    object(stdClass)[1]
      public 'charset' => string 'utf-8' (length=5)
      public 'text' => string 'Wushu inform - Sacensibas Igauni' (length=32)
  1 => 
    object(stdClass)[2]
      public 'charset' => string 'default' (length=7)
      public 'text' => string '	' (length=1)
  2 => 
    object(stdClass)[3]
      public 'charset' => string 'utf-8' (length=5)
      public 'text' => string 'ja (Tallina), б�аОб�аЕаВаНаОаВаАаНаИб� аВ аЂаАаЛ' (length=48)
  3 => 
    object(stdClass)[4]
      public 'charset' => string 'default' (length=7)
      public 'text' => string '	' (length=1)
  4 => 
    object(stdClass)[5]
      public 'charset' => string 'utf-8' (length=5)
      public 'text' => string 'аЛаИаНаЕ 11 аДаЕаКаАаБб�б�' (length=26)