DUBLIN (Reuters) -Ireland said on Wednesday it would mount a legal challenge against Britain over a new law giving conditional amnesties to former soldiers and militants involved in decades of violence in Northern Ireland. Britain has halted prosecutions of those involved in three decades of bloody conflict in Northern Ireland, saying they are unlikely to succeed and an independent body should be set up instead. Victims’ families, human-rights organisations and all major political parties on the island of Ireland – including British unionist and Irish nationalist – have condemned the law which…