Fixed a compilation error in MSVC <= 2012

Special thanks to Angelmelody

Signed-off-by: Haru <haru@dotalux.com>
Add prefix char_ to most functions in char.c
Add prefix inter_auction_ to most functions in int_auction.c
Add prefix inter_guild_ to most functions in int_guild.c
Add prefix inter_mail_ to most functions in int_mail.c
Add prefix inter_mercenary_ to most functions in int_mercenary.c
Add prefix inter_party_ to most functions in int_party.c
Add prefix inter_storage_ to most functions in int_storage.c
Add prefix inter_ to most functions in inter.c
Add prefix pincode_ to global variables in pincode.c
Split functions in int_mail.c.
Split functions in char.c.
Split functions in int_quest.c.
Split functions in inter.c.
Add most functions from char.c to interfaces.

Introduced interfaces: chr, mapif, loginif.
Add most functions from int_auction.c to interfaces.
Add most functions from int_elemental.c to interfaces.
Add most functions from int_guild.c to interfaces.
Add most functions from int_homun.c to interfaces.
Add most functions from int_mail.c to interfaces.