Rockbox

This patch reworks the handling of the replaygain metadata. The goal is to save space in id3v2buf and to save some binsize. The svn implementation uses two independent representations for gain values: (1) an integer value which can directly be used by our dsp-code and (2) a string representation. The string representation is only used by WPS/screen for display purposes. To keep the string representation id3v2buf is used (9 bytes per gain).

Main idea of this patch is to fully remove the string representation and perform a snprintf() based on the integer representation when needing it for WPS/screen purposes.

In consequence the integer representation cannot be saved in a ready-to-use format for the dsp-code. When handing over the gain to the dsp-code convert_gain() must be called. Through dropping the string handling the replaygain related code became smaller (~300 bytes for a nano 2g).

As a bonus a svn bug is fixed that displayed wrong replaygains when parse_replaygain_int() was used to set the gains (used by mpc and ID3v2.4 tags).